There's over the top. There's way over the top. And there's Jim Carrey.

No question — he's Jerry Lewis to the 10th power.

But there's also no denying that "Liar Liar" is hysterical. (Albeit too vulgar for children.)

It's certainly an old joke to mix up the words "lawyer" and "liar," and one might think that building an entire movie around that joke would be stale indeed. But Carrey and company manage to put a fresh spin on the subject, using a fantasy twist.

Carrey plays a conniving lawyer who has been lying for so long that it's become second nature. He's so good at spinning fabrications that one of the partners (Amanda Donohoe) in the firm where he works has an eye on him to become a partner.

But lying for a living has taken its toll. Cheating on his wife (Maura Tierney) cost him his marriage two years earlier, and now he is constantly disappointing his young son (Justin Cooper) by making promises he has no intention of keeping.

So, when Dad doesn't show up for his son's fifth birthday party, the boy makes a sincere wish — that "for only one day, Dad couldn't tell a lie."

Naturally, the wish comes true — but it also goes one step further. Not only can Carrey not lie, he's compelled to tell the truth.

What makes this truly funny isn't so much Carrey blurting out his true feelings without realizing what he's doing, but his own reactions to having done so. When he is seduced by Donohoe and she asks how he enjoyed their night together, Carrey says, "I've had better" — then gets a horrified look on his face. That look is what makes the situation funny.

Things progress gradually, as Carrey finds himself telling people how he really feels about them — from his co-workers to his mother. And eventually he finds himself telling the truth in court, specifically about a sleazy client (Jennifer Tilly) he's representing in a high-profile divorce case.

There are many memorable scenes, with Carrey performing slapstick that is almost on a par with Jackie Chan's comic stunt work (although it's more frantic than choreographed). Carrey is particularly manic when he beats himself up in a courtroom lavatory.

(Sadly, many of the film's best gags are in the theatrical preview, and it was interesting to observe the surprisingly muted laughter during these scenes, indicating that too many in the audience had already seen them.)

But it must also be said that, despite an endorsement by the teenage audience that will make this movie a huge box-office hit, "Liar Liar" is quite raunchy and vulgar. And that's really too bad, since the film could have been just as funny without all the sexual and body-function references.

As for Carrey himself, he's certainly the Rubbermaid Man, and he's amazingly talented at both slapstick and verbal comedy. But here, some of his quieter moments — what few there are — become the film's most effective, suggesting that less really is more.

If only Carrey could understand that he would still win over his audience without trying so hard. And maybe he'd widen it as well.

"Liar Liar" is rated PG-13 for sex, vulgarity, profanity, partial nudity (particularly Tilly, who seems ready to burst out of her blouse at any moment) and violence.