It's no trick to see why Hilary Swank, having won the Oscar for her fearless, inspired, gender-melting performance in ''Boys Don't Cry,'' should choose The Affair of the Necklace as her follow-up vehicle. Set amid the decadent French monarchy on the eve of the Revolution, the film allows Swank to cast her image back to an era when men and women occupied roles as corseted as their clothing; it's her not-so-subtle attempt to reassert her femininity in a ''prestige'' chick flick. As Jeanne de la Motte-Valois, a desperate comtesse who lies and schemes her way through Versailles, all to acquire a 2,800-carat diamond necklace that will let her win back the honor of her fallen family, Swank is playing yet another born deceiver who hoodwinks people only because she's a tormented ideal- ist. It's flawless conceptual casting, but the transplant, I'm afraid, doesn't take. The moment Swank appears, her androgynous rock-star lips framed by an unflattering mass of dollish curls, she looks tentative and uncomfortable, like Alanis Morissette trapped in a bad period-piece video.
It turns out that Swank isn't great at clipped refinement. There's something eerily earnest about her -- the blank modern voice, the eyes aglow with sincerity -- that renders her all wrong for a costume drama pitched in the arched-eyebrow invective mode of ''Dangerous Liaisons.'' Then again, it doesn't help that the liaisons here feel about as dangerous as a portfolio of mutual funds.
Jonathan Pryce, who always looks as if he's having dirty thoughts about how to water the garden, is Cardinal de Rohan, France's chief religious bureaucrat, a debauched libertine eager to wriggle back into the good graces of his enemy, Marie Antoinette (Joely Richardson). Jeanne, trying to convince him that the queen has come around, concocts a series of fake letters and enlists a trio of coconspirators, played by actors who seem to be competing in the ''Masterpiece Ham'' sweepstakes. Simon Baker, as Jeanne's gigolo lover, at least minces in period, but Adrien Brody plays her surly husband with incongruous De Niro smirks and smolders, and Christopher Walken, as some sort of mystic con artist, talks like Dracula and sports a hairpiece that threatens to devour his head.
Directed by the veteran light-comedy hack Charles Shyer (''I Love Trouble''), from a script by John Sweet, ''The Affair of the Necklace'' is slipshod rather than sly. There's no fury to the movie, repressed or otherwise, which may be why when the Revolution arrives, it has all the impact of a guillotine with a deadly dull blade.