Jim Carrey entertains himself mightily, and his enthusiasm is infectious. He plays Fletcher Reede, an unscrupulous attorney whose son makes a wish that Dad stop lying for 24 hours. The wish comes true. Suddenly, Fletcher can't lie he becomes incapable of spitting out anything but the truth, no matter how rude or embarrassing. Carrey, tying his face in knots, is like a man in a straitjacket: The more he tries to lie, the harder the truth straps him in. The story is straight out of a Chevy Chase movie, but Liar Liar isn't a ''family'' comedy or even a real satire. Its central relationship is the one between Jim Carrey and himself. B

