Judging by Crossroads, her film debut, recording superstar Britney Spears is not an ingenue and not yet an actress. However energetically she tosses the gold-plated locks, flashes teeth like neon pearls, and shakes those quicksilver hips, the result plays less like a coming-of-age romance than an infomercial.

Happily, the product pitched here is not Pepsi, the libation to which she is commercially wed, but rather the pop songstress' self-titled third album. Her hits "Overprotected" and "I'm Not a Girl, Not Yet a Woman" feature prominently in the film about the high school valedictorian who sheds her goody-goody image and takes a road trip to find her estranged mother.

The best that can be said of Spears' maiden film voyage is that it is not an unmitigated disaster like Glitter, pop canary Mariah Carey's bomb of last year.

The movie introduces Lucy (Spears) as a daddy-dominated daughter eager to break free and discover her own voice. Curiously, Spears is considerably less enthusiastic in finding Lucy's voice than she is in singing along with songs by Madonna ("Open Your Heart") and Joan Jett ("I Love Rock 'n' Roll").

Tricky business, the screen career of a pop star. The qualities that give Spears' musical persona urgency and currency - her seesaw between wholesome tease and vampy tramp - are enjoyable in the three-minute increments of a pop song.

Sustained over a 90-minute film, this back-and-forthing begins to seem less like a teen 'tween girlhood and womanhood than a mature marketing powerhouse exploiting a transitional developmental moment.

A pop star who wants to be a movie star has two choices. Like Elvis in Jailhouse Rock or Prince in Purple Rain, she might get filmmakers to customize a vehicle for her unique persona. Or like Madonna in Desperately Seeking Susan and Mandy Moore in A Walk to Remember, she might try to create a character.

In this film directed by Tamra Davis, Spears jumps between both options, which makes for an inconsistent film. Instead of getting a customized vehicle, she takes several different models out for test-rides. She does the virgin thing. Then she does the tramp thing. And then the love thing. (Parents be advised that her character has a relationship consummated offscreen.)

While Spears can be in character for the length of a music video, judging by Crossroads she hasn't yet learned how to build a performance that has forward momentum. This is a star vehicle that stalls.