Think of "White Chicks" as a crude parody of Billy Wilder's "Some Like It Hot"; it could be called "Some Like It White." It's about a couple of disgraced FBI agents who transform not only their gender, but also their ethnicity until they have become the creatures of the title in order to crack an extremely lame kidnapping conspiracy.

But it's not what the Wayans brothers do, it's how they do it. They do it funny. Older sibling Keenen Ivory directs, younger siblings Shawn and Marlon co-write with him, and Shawn and Marlon star. Do yourself a favor and take an extended $27.95 popcorn-and-Coke break in the lobby during the flatulence-in-the-fancy-restaurant bit and you might find yourself happier going out than when you went in.

Almost nothing formal in the film works. By formal I mean little stuff like, oh, you know, plot, setting, character, believability of milieu, dialogue, conviction of central device. So what's left? Well, the Wayans brothers going downtown way uptown.

They play feeble Feebs named Marcus and Kevin Copeland, whose job performance has them on the edge of getting fired. Finally given the low-strain task of driving two rich blond sisters to the Hamptons, where they will be put under protective observation as a way of capturing a kidnapper, they have a minor accident and each of the high-strung girls receives a minor facial laceration. Since the girls are spoiled, trivial, silly, vain, ignorant and sullen, they refuse to appear in public with bandages and instead decide to spend the weekend in a New York hotel.

So the brothers use the FBI's disguise technology to masquerade as the two sisters. They will go up to the prissy glades of far Long Island and sport with the preppies, the millionaires, the celebs and the wannabes who've turned that neck of the woods into the world's most exclusive creep zone.

Now, as a movie illusion, this just never begins to work. The two don't look a thing like white chicks. They don't look like black men, either. They sort of look like they come from the future: rubberized robotoids from the planet of the really cheesy special effects. Their faces aren't turned white cosmetically, but planted under rubber cheek forms; the result is dead, dead, dull, inexpressive, rendered yet more "I, Robot"-like by blond wigs that look like skinned poodles that have been soaking in the Tallahatchie River for years.

But as a premise for some good, tough sketch comedy, the device is brilliant. It affords us a look into a world through strange eyes. When one of them encounters a girl in a dressing room, you think: Oh, here we go, cheap boob jokes. But that's not it. What he discovers is a young woman crippled by body anxiety, tormented by three extra ounces that she sees as ruining her body and her life, since her life is her body.

That's a continuous surprise in the film: the Wayanses, so immature in so many ways, don't use their entree into girl world for tawdry purposes. Quite the contrary, and sometimes even movingly, they become anchors of faith and self-belief, almost psychological medics who apply instant first aid to the many, many wounds of bitter girl combat.

A continual joke is that as black men, strong and body-confident and well-versed in dynamic improvisatory verbal traditions, they make superb white chicks. They're smarter, faster, tougher than the rest of the gals and, affiliated with a lesser clique, they lead their crew to social triumph. And when the white boys condescend to them or cop attitude on them, the boys get a lesson fast.

That's what's so good about "White Chicks," and often so funny. What else is good about it? Er, nothing.

White Chicks (105 minutes, at area theaters) is rated PG-13 for drug-related humor, plus a revolting bathroom-joke sequence.

Shawn Wayans, left, and his brother Marlon go undercover but hardly look like the rich white sisters they are supposed to be in "White Chicks."