Spears, who turns 21 on Dec. 2, was flaunting her inner grownup, turning to the makeover queen of couture for a quick fix. "She wanted something sophisticated and glamorous," Versace said.

It was the culmination of Spears's two-month intermission from work, ostensibly to relax but in reality to begin the process of refashioning herself for a new career. It will take more than one body-hugging dress and some nude chiffon to do the job.

Spears, who made her debut as a wholesome bubblegum star with a penchant for sweetly flashing her belly button, is faced with a problem: the qualities that made her accessible and popular as a teenage star may be precisely the ones choking her career as an adult, leaving her looking like a parody as she tries to become a grownup recording artist.

The movement she led, said Craig Marks, the editor of Blender, the music magazine, is "very five minutes ago."

"She needs to come back with a new second act," he said.

While Spears has sold 52 million albums worldwide in the last four years, sales have nose-dived, from 24 million for her first album, to 19 million on the second, to nine million on Britney, which was released last November, according to her manager. For any other artist nine million would be a blockbuster, but for Spears it shows her popularity has seriously eroded.

Her appeal with listeners on radio is waning, too. Tom Poleman, program director for Z-100 in New York, perhaps the most influential Top 40 radio station in the country, said his station played the sultry 2001 single "I'm A Slave 4 U" fewer times than any of her previous singles. "We played it, but it didn't have as much staying power," he said.

Brandon Holley, the editor in chief of Elle Girl, said she gets e-mail from hundreds of teenage readers about Spears, whom the feminist author Camille Paglia once described as "Lolita on aerobics."

"They are really tired of that sausage-casing look, that busting out all over the place, and they are very anti-midriff right now," Holley said. "It's a Britney backlash."

It is a pop-star crisis shared by a number of her peers, including Christina Aguilera, 'N Sync, the Backstreet Boys and a host of Britney clones, as they try to make the often hazardous shift from teen idol to adult superstar without alienating their loyal fans.

Spears has been challenged by a raft of grittier teenage singer-songwriters who play guitar and wear dime-store T-shirts and ties instead of snug bustiers.

Dubbed the "anti-Britneys," they include the tough rocker Pink, the soulful Michelle Branch and Canada's Avril Lavigne, young women who eschew the overt yet out-of-reach sexuality Spears has cultivated. Holley said Lavigne and Branch in particular have replaced Spears among her readers.

From the looks of things, the Britney backlash has been picking up speed. Two executives who have worked with Spears said they were dismayed to see insinuations in the tabloids that she is facing a Mariah Carey-like emotional breakdown.

Her personal life has also been troubled. Her parents divorced this year, and she broke up with her boyfriend, Justin Timberlake of 'N Sync. Her aunt, with whom she is close, is being treated for ovarian cancer.

"She is not having a breakdown," said Larry Rudolph, one of her managers. "This is a girl who has been on the most unimaginably wild roller coaster ride for the last five years without a break. She was going to stop being the public Britney Spears and start being the private Britney Spears."

Her handlers say that over the last two months she has been trying to live like any 20-year-old — albeit one who has grossed $40 million to $50 million U.S. a year for the last four years. She has been doing yoga and going shopping. She is not hanging at the mall but at the spring fashion shows in Manhattan and Milan. (In Italy, Spears selected several Versace outfits and received the usual treatment accorded big celebrity guests: the designer paid.)

Versace — who also restyled Baby Spice and Chelsea Clinton — invited the singer to spend five days as a guest of the Versaces at their villa on Lake Como. She is not confused about the need for change, Versace said. "She's very, very sane."

Next week, Spears will return to the recording studio in Los Angeles, "looking at new ideas," Rudolph said. "She knows she will be changing."

There are no set plans for the next album, but Rudolph said Spears might take a more overtly sexual approach, echoing songs on her recent album, like "I'm a Slave 4 U" and "Boys."

Her break was probably well-timed, said James Harris III, the producer known as Jimmy Jam, who has worked with Carey and Janet Jackson. "The thing I found is an artist has to have a chance to live life. As we saw with Mariah, if you don't shut down it gets the better of you."

To be sure, pop culture history is thick with the stories of teenage stars who aimed for longevity but saw their high-flying careers evaporate.

Spears almost missed adolescence altogether. At 11, she moved to New York with her mother and younger sister, leaving her father and brother behind in Louisiana, to join the cast of The Mickey Mouse Club. There, she met Timberlake, a fellow member, who later joined 'N Sync and dated Spears.

In 1999, Spears posed for Rolling Stone magazine wearing short shorts in her childhood bedroom in Kentwood, La., crowded with stuffed animals. A Mississippi group, the American Family Association, promptly called for a Britney boycott.

Unlike Aguilera, who made her debut at 18 and whose new album, Stripped, will be released this month, Spears did not make sex a part of her act.

Aguilera's first video from Stripped makes Spears's "I'm a Slave 4 U" "look like play school," said Atoosa Rubenstein, the editor in chief of Cosmo Girl magazine.

The epitome of reinvention for any diva-in-waiting is Madonna, who has offered herself to audiences dressed as a Marilyn Monroe platinum blonde, a nun, a mistress of sadomasochism, a Vargas pin-up, a cowgirl and, on a recent cover of Vanity Fair, a World War II flyboy.

"It takes an extraordinarily confident individual to be secure and allow for change," said Lyor Cohen, chief executive of Island Def Jam Music, who last spring signed Carey to a three-record deal. "That is why Madonna is successful. She embraces it."

Unless Britney can match Madonna's endless morphing, the most celebrated diva of Generation Y may become a one-era wonder. She has been visiting with Hollywood film executives and is eager to expand into movies with "A-list stars," Rudolph said, but her next announced commitment is to a role in a movie about Nascar racing — hardly a vehicle for Oscar stardom.