At the age of 20, she has exponentiated. She long ago established herself, according to the accountants, as 'the bestselling female artist during any one-week period in music history'. What's she worth? All I know is that she coolly scoffed at the $10 million proffered by an American businessman who wanted to have sex with her. She has become a collective fantasy, whose image inflames cyberspace. Search engines spend much of their time servicing requests for 'Britney naked'. One internet site compounds 1,001 other Britney sites, each of which opens into labyrinthine photo-galleries and encyclopaedic libraries of tittle-tattle.

With 17 million copies of her new CD sold, she is about to synergise. Her first film, Crossroads, a sorority road movie, opens next month. She has also published a fluffily inspirational first novel, A Mother's Gift, co-written with her gooey mom, Lynne, who once taught school but has 'taken time off to be her daughter's biggest fan' (which means, I suspect, going on the payroll).

The marketers turn all cosmic when describing Britney: she is 'the planet's biggest megastar'. The sun itself revolves around her. Her tour bus has a tanning salon, so she can treat herself to heliotherapy and honey-tone her skin when on the road between gigs in the middle of the night. Britney says that she intended 'to be big all around the world', and her chest has expanded to keep up with her ambition. Wherever you look, she is there - inside my head, and also lurking, as I discovered, in every letter of the alphabet.

A is for America, which Britney nubilely, precociously, go-gettingly embodies. The country is a permanent adolescent like her; she enacts its brash, mercenary dreams and its constitutional guarantee that everyone's wishes will come true. 'Go for what you want,' her mother told her when entering her in television talent quests at the age of nine. On 11 September, she was flying across the Pacific to Australia. Aware of her patriotic obligation, she immediately returned home to comfort her people and, given the amount of flesh she customarily exposes, to taunt the dress sense of all those dowdy, covered-up Afghan frumps. 'I think America is the best country in the world,' she announced. 'I really do.'

B is for Brittany, which is perhaps what her parents - back in those benighted days before we had SpellCheck to help us - named her after. To her family, she is known as Brit-Brit; if only to maintain the alliterative beat, she once had a Yorkshire terrier called Bitzi, though the dog may, given Britney's fondness for scanty threads, have been named in homage to that 'itsy-bitsy teeny-weeny yellow polka-dot bikini' in the ancient pop song.

Britney believes in her own manifest destiny, and her name may also explain her designs on British royalty. Her email flirtation with Prince William ended when she arrived for a meeting to be told by a sentry at the palace gate that he was out hunting. Britney, who can be vixenish on occasion, slunk away, her brush between her legs. Nevertheless, she remains fond of Britain - she adores 'the shopping, and your accents' - and has built a mansion in Louisiana for her mother that is 'all Tudor, like a British house'. It even has an Elizabethan-themed media-room.

We enjoy favoured status, since in Britney's world, other countries consist mostly of hotel suites. However, the heroine of A Mother's Gift plans a customised grand tour. Her boyfriend wants to 'race on the autobahn in Germany' and 'eat pizza in Rome', while she intends to visit Austria because she has heard that this is where they made The Sound of Music, her 'favourite movie of all time'.

C is for Cola, Pepsi to be precise, which paid Britney £63,000 per second to jive and jiggle through the commercial breaks on this year's Superbowl telecast. The show concluded with her performance of an anthem entitled ''The Joy of Pepsi'. She is canned effervescence, with rip-tops strategically positioned all over her costume.

D is for Dolls, which Britney collects and also merchandises. There are those who think she is one herself, like the inflatable ladies they used to sell in Times Square novelty shops. Singing 'Hit me bay-bee one more time' or 'I'm a slave for you', she plays at being an S&M Barbie. You can buy your own Britney, position her plastic limbs at will or have her do striptease routines. When she met Madonna's daughter, Lourdes, the shy child asked her assistant (even pop kids have PAs) to whisper a message in Britney's ear. 'She has all your dolls,' said Lourdes's lady-in-waiting.

E is for Evil, which Britney incarnated at the age of 11 when cast as a diabolical infant in a Broadway play based on the horror film, The Bad Seed. She shrieked, hollered and rampaged through the theatre in a fit of devilish ecstasy. The hypothesis of demonic possession intrigues me. Frank Skinner showed a clip from one of her pre-pubescent concerts during his recent television interview with Britney. A sonic cyclone issued from the tot's braced teeth, booming in the contralto register as she gave vent to an age-inappropriate lament about unrequited passion. 'There's a slight element of The Exorcist about this,' Skinner remarked with a shudder. Britney, engagingly inane as ever, wailed: 'Oh my gosh, oh my goodness, oh my Gaaaahd!'

F is for Fan Base. Those battalions of randy teens are intrepid. Britney has moved her family to their new Tudor ranch-house inside a gated community because her customers, as if seeking holy relics, used to invade the front yard of her former home and carry off clods of soil. 'I mean,' Britney asked, 'what do you want with dirt?' I just can't imagine.

G is for Geek and Goob, which Britney sometimes calls herself, as in 'I'm just, like, this geeky person from Mississippi' or, when she wore a tanktop with flannelette pyjama pants to an interview, 'I look like such a goob'. On other occasions, she will define herself as 'a total dork'. She's right in all cases: remove the make-up, send the stylists home and you unveil a gawky, inarticulate teen with a big nose, teeth that resemble the radiator of a 1950s Cadillac and vacant, unfocused eyes. It's a mystery.

H is for Horse. Britney does not ride, but could once be seen - thanks to some digitally manipulated pixels - enjoying equine sex in a remote corner of the internet. Is it for this that Al Gore invented the information highway?

I is for Implants, euphemised by Britney as ''that whole boob thing''. She denies having been pumped full of silicone, and says: 'I just grew.' Soon after the presumed procedure, she was back on tour, announcing: 'I can't wait to come to England and show my English fans an awesome set.' This turned out to be a reference to the songs she'd be singing. Or is her voice an implant, too? She also denies lip-synching at concerts. 'I'm singing my ass off,' she insists. 'I'm, like, totally live.'

I wonder. Britney also calls her film, Crossroads, 'really real', though, of course, it's a comforting fantasy in which all problems are promptly resolved, and stardom and happiness both come automatically so long as you desire them intensely enough. Britney's sense of reality is, to say the least, relative. In A Mother's Gift, people and places are recurrently compared with fictitious prototypes: an office is 'like something from a TV show' (which absolves Britney the novelist from the bother of describing the room) and a snooty woman has 'the moneyed look that villains had in movies'. But this counts as realism of a kind, since Americans spend so much time imitating or aspiring to resemble characters in sitcoms.

In interviews, Britney repeatedly says: 'I'm a real girl' or: 'I'm for real', as if hoping to convince herself. Like her breasts, she both is and is not. This little person is also, as she admits, 'a show business product', designed to occupy a lucrative commercial niche: a bionic amalgam of flesh and financial engineering. The boob thing sums up the conundrum. A myth is a lie that tells the truth.

J is for Justin Timberlake from the boy band *Nsync, who is Britney's sweetheart. They page, they text and, when she calls him, she often says she'd like to wriggle down the telephone wire, squirm out through the receiver, and clamber inside his face. Even so, Britney has confessed that Brad Pitt is 'like, the ultimate', and she once challenged Ben Affleck to a game of strip poker. Queues of contenders wait to fill any vacancy: on the internet, there's an oversubscribed site for Future Husbands of Britney Spears.

K is for Kinesiology, in which Britney's brother, Bryan (as I said, it's an alliterative household) majored at college. Don't ask me for details of the curriculum. Maybe it involves the study of Britney's piston-pumping, arm-flailing dance routines. On the family's website, her mom reports that Britney recently had tuition in 'soccer skills' to prepare her for her Superbowl appearance. As for academic credentials, Britney herself was 'home-schooled', though she makes amends by despatching her heroine to college in A Mother's Gift and having her take a class in 'World Lit'. This, presumably, is like World Music with the amplification turned down.

L is for Lolita and Lubrication, which go together. Britney defines herself as a nymphet in Crossroads: 'I'm not a girl but I'm not yet a woman,' she caterwauls. Though she has sternly said: 'I don't want to be part of someone's Lolita thing', one of her handlers must have studied Nabokov's novel. Humbert, absconding with his underage stepdaughter, sees double entendres everywhere, even at petrol stations: 'A garage said in its sleep - genuflexion lubricity; and corrected itself to Gulflex Lubrication.' In Crossroads, Britney's dad owns such an establishment, and as she skips town with the stubbled hunk who later deflowers her, she casts a backward glance at the sign which offers - I swear it - lube jobs. The snake, as Nabokov knew, was wriggling through the garden long before the fall.

M is for Moroccan vibe, which is how Britney describes the decorative style of her Los Angeles pad. Inside, impersonating a harem girl, she slouches around in flip-flops and those flannel jammies. She likes sultry climates. 'When it's hotter,' she reasons, 'you tend to wear less clothing.'

N is for Na-Na-Na-Na-Na, the first line of a song in Crossroads, based - as Britney proudly points out - on one of her own poems. She thinks the heroine is 'like me because she's always writing. Sometimes the words come to me when I'm, like, in the bath or stuff'.

O is for Octaves, of which Britney possesses four. The heroine of A Mother's Gift, hauled out of bucolic poverty by a scholarship to a musical academy, thrills to the Moonlight Sonata, which she recognises from a detergent ad, and ponders a motto by Thomas Carlyle on the school's cupola, which claims that music is the speech of angels. Britney's notion of the art she practises is somewhat less ethereal. Her favourite line of movie dialogue comes from American Pie, where a raunchy teen boasts: 'One time, at band camp, I stuck a flute up my pussy.' Is this what Britney means when the girl in her novel reaches 'a place only music could take her'? Wherever the breath comes from, Britney's body sings.

P is for Prayer, in which Britney places a reverent trust. A sign in her Louisiana neighbourhood benignly advises: 'Drive Carefully, Live Prayerfully.' Every night before she sleeps, she does what she calls 'my devotional'. God pays particular attention to Britney's murmured nocturnal requests, and, like an obliging aerial DJ hosting a phone-in programme, immediately answers them. 'I would pray "I hope my song plays on a certain radio station that's really big", and it would happen. Then, "I hope they play the video on MTV", and they did.' Our Father once reached down from heaven to grab Britney's leg and pull a muscle in it during a dance routine: 'I think it was Him giving me a sign that I needed a break. I thank Him for it.' Not since Jacko suffered so many little children to come unto him has a pop singer enjoyed so close a relationship with her maker. In A Mother's Gift, Britney awards herself a miraculous birth - well, actually a Nativity - which, of course, takes place on Christmas Eve. The Pope has invited her to contribute to an album of Christmas prayers. So far, Britney has not mimicked Madonna by masturbating with a crucifix, but if she did she would probably have divine approval. Can God be a dirty old man?

Q is for Quotations, inspirational slogans copied by Britney into her Prayer Journal. This chronicles her 'spiritual journey', the celestial equivalent of the more carnal car trip in Crossroads, which leads from Louisiana to California where Britney at last surrenders her expensive virginity. 'I have a lot of wisdom,' she world-wearily claims. 'I've had a lot of lifetime experiences.' All the same, I suspect that the thoughts in Britney's breviary will not require much chewing. As she says of the girl in A Mother's Gift, 'her mind was a bowl of mush'.

R is for the Republican Party, which dotes on Britney. During the election campaign in 2000, a Bush aide called her 'one of our greatest assets'. Bob Dole, also running for the Republication nomination, dosed himself with Viagra and appeared gloating lecherously in one of her Pepsi commercials. She sells herself as zealously as any politician: in the summer of 1998, she appeared at 26 shopping malls across America and, after one concert in Massachusetts, she managed to greet and pose for photographs with 300 family groups in only 25 minutes. It's this merchandising operation, swollen by deals with Sunglass Hut and Tommy Hilfiger as well as Pepsi, that the Republicans admire. Britney sometimes refers to 'my package'. By this, she does not mean the straining tops and jutting bottoms she wears but to her product profile, her demographic reach and her market penetration. Britney is global capitalism in a micro-mini.

S is for Satisfaction, denied to Mick Jagger. When Britney met him, she recoiled from his kiss as if confronted by a crumbly, decrepit vampire. Nevertheless, she has recorded Jagger's song, primly detoxifying its lyrics. Jagger spurns the pitch of a washing-powder salesman because 'he doesn't smoke the same cigarettes as me'. Britney doesn't need the phallic prop as a means of self-definition. In her version, she resists the importuning of a girl on TV who 'tells me how tight my skirt should be', because 'I got my own identity'. Britney often tells her adolescent constituents to be proud of their sexuality, though she then confusingly adds that they should not have sex before marriage. This paradox will be more closely inspected further down.

T is for Totally, Britney's favourite adverb. After taking delivery of freebies from Hilfiger, she reported: 'My mom and my sister are like totally walking around in Tommy stuff.' Asked whether she and Justin understood each other, she cooed: 'We totally do.' And, with a grateful glance at the sky, she once asserted: 'I am totally blessed.' She has every right to appropriate the word. She is, after all, a totalitarian phenomenon.

U is for Umbilical Piercing. A diamond stud twinkles in Britney's navel (and, while we're taking physiological inventory, she also has a daisy tattooed on her toe). Her tummy bud is an innie, not an outie, so the incision was excruciating. 'I guess I don't have a good flap,' she said afterwards. 'You're supposed to have a flap of skin that's thin, but mine's thick.' Can't you just feel her pain?

V is for Virginity, which Britney prizes and has sought to preserve. Supporting the sacred pledge made by the young Christians who adhere to a cult of chastity called True Love Waits, she famously but non-committally said: 'I want to wait to have sex until I'm married.' Then, sounding increasingly less convinced, she added: 'I do. I want to wait. But it's hard.'

Her defloration, so agonisingly delayed, at last occurs in Crossroads. She first rehearses with an anaemic nerd who shares her Bunsen burner in chemistry lessons, but scrambles out of bed after a sneak preview of his puny rig. On the road with her girlfriends, she plucks up courage in a giggling discussion of what it's like 'to touch one'. Her own hands, at this stage, have still not made contact with hydraulic tissue. Consummation finally occurs at Santa Monica, as an engorged, torrid sun plunges into the Pacific and breakers foamily thrash on the beach. The chosen one is the roughneck in greasy denim who, fresh out of jail, drives Britney and her chums across the country. As he shucks off his shirt and spreads himself on top of her, we see the tattoo that qualifies him for the task - a pair of Mephistophelean wings, sprouting on his back. It is a truly supernatural moment. The Baptist babe has given herself to a fallen angel, who may be the bearer of the above-mentioned bad seed. If they felt the earth move beneath the motel bed, it must have been the San Andreas fault tearing open to protest at America's loss of innocence.

W is for Wedding. Never mind about the devilish scenario described in the previous entry. Britney's marriage will be pantheistic, since she intends to wed the universe (having already coupled, at least in their imaginations, with a goodly proportion of the men in it). 'I would like an outside wedding,' she confides. 'On the beach, really beautiful. Barefoot, you know. Like, really simple.'

X is for XXX, which is what some think Britney should be rated. In one of her concerts, she made callisthenic love to the kind of pole lapdancers like to impale themselves on, and in Crossroads she performs in a karaoke bar wearing spiked-heel boots, ravished cut-offs, a studded belt and a threadbare T-shirt with FREEDOM emblazoned across it. For a Rolling Stone session with the photographer David LaChapelle, she seethed in her frilly bedroom as if it were a tart's boudoir, then went outdoors to push a tiny bicycle wearing tinier shorts with BABY spelled out in diamanté across one of her butt cheeks. Prudes classify Britney as kiddie porn.

Y is for Y-Fronts, which she dances in at the beginning of Crossroads. The scene sums up Britney's teasing appeal: she is singing in her bedroom, using a spoon as her microphone. We suspect that she is secretly pigging out on ice cream, which in calorie-conscious America is synonymous with sin. But no, she's feeding from a bowl of blameless cereal. Her dad puts a stop to the little orgy by bringing in her academic gown, cleaned and pressed for her high-school graduation ceremony, and reminding her that she is bound for medical school. Dr Britney - now there's a thought! And here's another: what's her father (played by the goggle-eyed Dan Aykroyd) doing in her bedroom in the first place? Forget his excuse about the dry-cleaning. He is there, I suspect, to represent the intrusive, impertinent middle-aged male gaze.

But back to the Y-fronts, which both reveal and conceal, hinting at what Britney lacks. The underpants are morally safe, because, by her standards, they're old-fashioned in their baggy modesty. Apart from thongs and sports bras, Britney has no use for lingerie. Her clothes - a rubberised catsuit, for instance, designed by the woman who outfits the felines in Sex and the City - are so minimal that they don't allow for any other layer beneath them. Suddenly Madonna, wearing those armoured foundation garments on top of her clothes, looks positively matronly.

Z is for Zits, known to those with British complexions as pimples or blackheads. Those pustular fried eggs are Britney's fatal flaw, and her mom travels in her entourage on perpetual zit alert. But it's mom whose cooking is responsible for those flare-ups: 'I eat grilled cheeses in all the big hotels,' sighs Britney, 'but no-one can grill cheese like my mom.' Britney is a dietary recidivist. Her heroine in A Mother's Gift unpacks her luggage at the swank academy from a Warholesque pile of tomato-sauce cartons; the girl's trailer-trash mom jokes that her recipe for tomato soup is ketchup plus water. 'I love junk food,' says Britney unrepentantly.

Which is just as well, because, come to think of it, that's pretty much what Britney is. Like junk food, she sells instant gratification and, in doing so, she triumphantly Americanises the supine earth. She should come wrapped in greaseproof paper, with a straw, or perhaps a flute, to make ingestion easier.

Peter Conrad teaches English at Christ Church, Oxford. His book on Orson Welles will be published next year.

Britney A-Z online edition: links by Luke Skrebowski. The Observer is not responsible for the content of external websites. Crossroads opens on 29 March. A Mother's Gift by Britney and Lynne Spears is published by Boxtree on 12 April.