''Lucky number 42!''

That's Diane Lane's half-joking description of ''Unfaithful,'' in which she delivers a career-defining performance that many critics have declared a revelation... 23 years and 41 movies after she was first declared a revelation, at age 14. Last July, when she was in the final days of the film's exhausting four-month shoot, she joked, ''I may never work again after this!'' Sitting in a Los Angeles bistro, a week before the film opens, she's become at least cautiously confident that the film will not mark the end of her career. She's also far more relaxed, having returned the previous day from a weeklong road trip. ''I was aiming for the Four Corners [where Arizona, Utah, Colorado, and New Mexico meet], but it would have taken too long to get back,'' she says. ''I still haven't washed my hair yet, but at least I've got my skirt on and am out of my jeans, that's an accomplishment.'' (For the record, with her elegant black skirt, V-necked shirt, and pinned-up hair crowning her delicate features, she hardly looks like she just rolled out of Stuckey's.) She's grateful that she was barely recognized in her travels: ''Maybe somebody somewhere will be like [she squints as if inspecting]. The nice thing is I can still go around and just be me.''

Those motel clerks and truck-stop cashiers are unlikely to stop at just a squint for much longer. After a decade of films overlooked (''A Walk on the Moon''), overhyped (''The Perfect Storm''), or just plain over (''Judge Dredd''), this underappreciated beauty and self-described ''actress for hire'' has finally been given the opportunity to show the megaplex crowd (and all of Hollywood) her exquisite range, wrenching between passion and guilt as a happily married housewife who plunges into a doomed affair. Richard Gere, her costar from 1984's ill-fated ''The Cotton Club,'' plays ''Unfaithful'''s cuckolded husband, and gushes, ''She was kind of a dazzling kid at the time [of 'Club'], but she's an even more dazzling woman now.'' Adds director Adrian Lyne: ''Diane breathes a certain sexuality. But she's sympathetic, and I think so many sexy women tend to be tough and hard at the same time.''

Lane is in a profession where self-promotion is integral to survival, where living a glamorous life -- and making sure the world knows -- can help a career more than actual acting skill. Yet a lifetime in the business has given the 37-year-old actress a reflexive suspicion of all things Hollywood. ''She's one of the rare beauties who isn't working it,'' says Tony Goldwyn, her ''Walk on the Moon'' director. ''Maybe that's why she didn't hit superstardom in her 20s. She wanted to be an actress. She just happens to be incredibly beautiful, but she wasn't out there struttin' her stuff in that way that the marketplace sometimes wants.... When I decided to hire her, I thought, 'No one knows what this woman can do.'''

And now, even with this performance poised to catapult her status from ''Well, what about Diane Lane?'' to ''Get me Diane Lane!'' she remains skeptical about her future. ''Very few actresses retain their luster or the reverence that was held for them at a certain point,'' she says. ''Retirement comes for most people at 65, but female actors are like baseball players. 'Okay, I'm gonna sell cars now, I'm 32.''' And it will take more than a lucky 43rd film to make her take her career for granted. ''I [always] think they're trying to recast me the first two weeks of a movie, I'm very insecure like that,'' she says. ''You know where it says 'Fire Lane' on a studio lot? I have to walk over that every day to get to the makeup trailer and I think, 'If you're gonna do it, today's the day.'''

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