When the most famous female singer to emerge in the past five years sashays down the red carpet at tonight's MTV Video Music Awards gala, she will be marking her last public appearance until ... well, she's not sure when.

Scheduled presenter Britney Spears announced recently that she is embarking on a professional hiatus. "I need this break to rejuvenate spiritually and to just play," she told People.

And who could blame her? At 20, Spears has sold more than 46 million albums worldwide and has emerged as one of the nation's most ubiquitous pop icons. Her toned midriff and aggressively produced, effects-laden chirping have launched a string of unavoidable videos, tours and ad campaigns for everything from milk to Pepsi. Her extracurricular ambitions were evidenced in the past year by a feature film, Crossroads, and a new Manhattan eatery called Nyla.

Significantly, though, neither the movie nor the restaurant inspired the kind of rapt attention that some had expected. Furthermore:

• Sales of her most recent album, Britney, are less than half of predecessor album Oops ... I Did It Again.
• While her concert revenues have held steady, her 2002 shows often were assailed for staleness and lack of innovation.
• Most alarming, the first three singles from Britney each received significantly fewer spins on radio than the corresponding tracks on her previous album, which showed a similarly negative pattern in relation to Spears' 1999 debut, ... Baby One More Time. And Britney's fourth single, Boys, peaked at No. 39 after three weeks on the top 40 airplay chart, despite an expected promotional boost from its presence in Austin Powers in Goldmember.

"Her music is not cutting through the way it used to in the '90s," says Dylan Sprague of Atlanta top 40 radio station WWWQ-FM. "She still has some true fans among very young females, but others have moved on to artists of more substance, like Michelle Branch and Avril Lavigne."

There also is speculation about how Spears is handling the challenges confronting her, not only as an artist but in her personal life. The breakup of her parents' 30-year marriage and the singer's own split from fellow teen idol and 'N Sync frontman Justin Timberlake made headlines this year, as did an incident in Mexico in which Spears aimed a middle finger at paparazzi surrounding her car.

Spears' representatives are, predictably, eager to discourage the impression of a traumatized or coasting star. A spokeswoman for her label, Jive Records, says the singer will spend some time writing songs for a CD due next year.

Personal publicist Lisa Kasteler adds that Spears plans to read movie scripts and meet with producers and directors. One project, described as a racing drama in which Spears plays the daughter of a NASCAR team owner, is being written.

"She's in perpetual motion," Kasteler says. "She's hardly disappearing."

But does she have a choice? "Acts like Britney Spears are concocted to appeal to the teenagers in their audience as idealized reflections of themselves, and that has nothing to do with music at all," says media critic and author Mark Crispin Miller. "Britney is like a figure in an ad campaign pitched at young girls. In five years, no one will be listening to her records, unless they do so ironically."

Some of those girls already are expressing wariness. "She's gone a little overboard in terms of what she's wearing and the subjects of some of her songs," says 16-year-old Melissa Gonzalez of Queens, N.Y. "And all the times I've seen her singing live on TV, she's lip-syncing. She'd be better off as a model than a singer."

Other followers remain stalwart. "I think her last CD really showed a maturing artist," says Matthew Gray, 20, of Manhattan. "It's not just about talent, it's about the look, the attitude, the whole package. I think she'll be around for a while."

Even a few of Spears' most ardent supporters believe the time is right, however, for teen pop's poster girl to lower her profile. "The downside to peaking early is when you don't realize you've reached a point of oversaturation," says Rik McNeil of top 40 station KFMS-FM in Las Vegas. "So it's a great time for her to take a break, then come back and reinvent herself."

But for many, the jury is out on whether Spears has the talent or temerity to take that next step. Most teen idols — think Tiffany, Leif Garrett, Bobby Sherman — do not enjoy long, fruitful careers.

"Unless you happen to be Elvis or The Beatles or Michael Jackson, you have about a three-to-five-year run," says veteran rock writer Dave Marsh.

Fans and industry observers who have compared Spears to a younger Madonna, noting her acting and entrepreneurial aspirations and penchant for captivating the media, may be influenced less by Spears' intrinsic appeal than the increasingly celebrity-obsessed culture that made her a star. "Whether anything of remote interest to humanity happened or not, Access Hollywood still has 30 minutes to fill," Marsh says.

"On the other hand, there's this category of people like Cher and Charo and George Hamilton who are famous for being famous, rather than for anything they really do," he adds. "Maybe Britney will become the youngest member of that group, so even if she isn't selling anything, she'll have a reporter tagging along."

Charles Figley, director of the psychosocial stress program at Florida State University in Tallahassee, says the combination of Spears' youth and her iconic stature makes her especially vulnerable to the dangers that teen stars often face.

"She is experiencing a deformity in her human development to the extent that she has never had a normal childhood or adolescence," says Figley, who studies celebrity stress in the context of family.

Indeed, Spears, whose mother helps manage her, has been performing virtually all her life, appearing as a Mouseketeer on television in 1993 and landing other professional gigs before that. "When fame comes," Figley says, it's easy to become addicted to it — "to develop this need to be noticed and adored."

In this respect, Spears' story could be contrasted with that of Madonna or the similarly ambitious and multifaceted Jennifer Lopez, who achieved fame as women in their mid-20s with fully formed, independent visions of what they wanted to accomplish.

"As a 25-year-old, you've had more life experiences that can give you self-worth," Figley says. "If you don't have that broader perspective to sustain you through hard times, it can be really tough."

Although Spears has sought to relay a greater sense of autonomy in recent projects, many continue to view the singer as a perpetual pubescent — another factor that may threaten her chances for longevity. Even as she approaches her 21st birthday in December, the media ponder her previous professions to virginity and raise a fuss if she is photographed with a cigarette or drink.

"Britney Spears ought to be placed in the category of child star, because she is still a commodity in others' hands," Miller says. Of reports that Spears' 11-year-old sister, Jamie Lynn, an actress on Nickelodeon's All That, is being groomed as her heiress apparent, Miller quips, "Yeah. Now they're coming out with a line extension."

Others argue that having an intensely involved, supportive family will benefit Spears in the long run. But the consensus is that the singer will have to assert her own voice more forcefully and convincingly to meet current media expectations and defy those who already have begun writing her career obituary.

"Radio has changed focus, suddenly favoring the anti-Britneys — "fully clothed young ladies who write serious, introspective songs and play instruments," Village Voice columnist Michael Musto says.

"Her next record will have to make a statement," Teen People music editor Matt Hendrickson says. "She'll have to write great songs and work with producers who can help her craft something that people will talk about."

Hendrickson believes Spears may be empowered by the solo debut that former boyfriend Timberlake is scheduled to release in November.

"It's a big leap for the most part away from the manufactured sound of 'N Sync," he says. "Given her powerful personal ties to Justin, that could help motivate her to also really try to stretch out."

Hendrickson has similar advice regarding her movie career: "I'd love to see her in a David Fincher movie — something well-written and twisted. She's in a position to take some risks, and she should."

Musto concurs. "Madonna's always been a master at picking the right trends and stylists to make her relevant to the new crowd, while Britney's more often been other people's puppet. But Brit will have to learn to take over the reins of her career and prove there's more to her than Vegasy oomph and a nice navel.

"If not, she'll be deemed a has-been in her early 20s — a fate worse than death."