NOT SINCE Audrey Hepburn's heyday has a star changed clothes as often as Jobeth Williams in "American Dreamer," a madcap comedy with Tom Conti as the guy with the Mastercard.

Those seven little words, "I haven't got a thing to wear," have come to stand for so much more than those three little words, "I love you." Now adventure begins when the heroine loses her bags and her psychological baggage -- like Karen Allen in "Until September," Kathleen Turner in "Romancing the Stone," and now Williams in this dual comic role.

As neglected drudge Cathy Palmer, she finds romance only in adventure novels. She's wife to a sexist prig (James Staley), mother to a couple of overly precious kids. And she has lots in common with the novelist heroine of "Romancing," who goes on a trip, meets a handsome guy and starts to live the plot of one of her novels.

Palmer wins a writing contest, goes to Paris to pick up her prize, gets amnesia and forgets not only her luggage, but her personality. She imagines she's one of her favorite fictional heroines -- Rebecca Ryan, a high-fashion sleuth with the derring-do of Indiana Jones and a "dozen dazzling costume changes," as the promoters say.

Meanwhile, she mistakes English playboy Alan McMann (Conti) for her paperback sidekick and gets him into a series of elaborate escapades that take them from the racks in the Conciergerie prison to the racks of Christian Dior.

Conti was an Oscar nominee last year for "Reuben, Reuben," in which he played a sarcastic, cruel womanizer. Here, he's warm, loving and protective, even cuddly, like an older Kermit the Frog. His savvy screen presence instantly turns what was a sluggish, domestic sitcom into classy comedy, the way Cary Grant always could.

Conti's the comedy cavalry. But Williams' metamorphosis, from drab and timid to glamorous and outgoing, doesn't come a moment too soon, either. Unfortunately her children remain a script problem throughout: She can't just fade into Conti's arms. She has to do something with those kids.

All the same, "American Dreamer" is a giant step up for writers Jim Kouf and David Greenwalt who collaborated on the sophomoric comedy "Class." This film, in the best tradition of mistaken identities and French farce, has some.

AMERICAN DREAMER -- At area theaters.