PERFORMANCES ASIDE, `JACK' CAN'T QUITE ACT ITS AGE, WHATEVER IT IS.

Byline: Amy Dawes Daily News Staff Writer

Wow, leave it to Francis Ford Coppola and Hollywood Pictures to slap an ending so sappy on ``Jack,'' a fantasy about a boy who ages at four times the normal rate, that it nearly wipes out the decent moments in the movie that lead up to it.

For, despite what you might fear from a movie this calculated, ``Jack'' isn't all bad. For one thing, it has Robin Williams, who's perfectly cast and quite winning in the role of the 10-year-old boy who looks like he's 40.

Williams (``Jumanji,'' ``The Birdcage'') has no problem calling forth his inner child. Performing with what is, ironically, a toned-down version of his usual manic energy, he gets it exactly right, from his shyness and easy tears to his exuberance and clumsiness. When his blue eyes light up with joy and he races home after a great day at school, he's pretty adorable.

There's also a vivacious turn by Fran Drescher as a clueless single mom who flirts with this poor man-child, and a delightful performance by Bill Cosby, who plays Jack's tutor, and who, as we all know, is great with kids.

But that's about all there is to absorb you in a movie with a premise this dubious and slight, and an outcome this predictable.

It starts with a hospital room delivery scene in which we learn that Jack's mother (Diane Lane) is giving birth to an 8-pound boy - after only two months of pregnancy! Doctors explain that this healthy child's cells are developing at four times the normal rate. By the time he's 10, he'll look like he's 40. And by the time he's 20 - well, we don't have to tell you.

Tutored at home until he's 10, Jack finally is sent off to public school (he has to shave in the mornings before he leaves), where he faces the taunts of the other children, but ultimately wins them over.

Often more poignant than it is funny, ``Jack'' walks an uneasy line between appealing to children and adults. The advertising is clearly aimed at children, as are certain scenes, like the flatulence contest among Jack and the real 10-year-old boys in the treehouse (10-year-olds, I guess, will like it).

Other scenes - like the one in which Jack ventures into a bar to try to pick up on the sexual advances he's been getting from Drescher (as his friend's mom, Dolores) - seem to come from a sadder, more adult-themed movie.

Coppola, the director, whose previous ventures into family filmmaking have included executive producing the much, much richer movies ``The Black Stallion'' and ``The Secret Garden,'' can perhaps be forgiven for succumbing to this one. He lost his son Gio in a boating accident when the youth was 23, and the movie's theme about the poignant fleetingness of life must have had personal resonance.

Still, when Williams delivers that theme in a mawkish closing speech, you wish that Coppola had found a more elegant vehicle for his sentiments.

THE FACTS

The film: ``Jack'' (PG-13; birth scene, some mature references).

The stars: Robin Williams, Diane Lane, Brian Kerwin, Jennifer Lopez, Bill Cosby, Fran Drescher, Adam Zolotin.

Behind the scenes: Directed by Francis Ford Coppola, written by James DeMonaco and Gary Nadeau, produced by Ricardo Mestres, Fred Fuchs and Francis Ford Coppola. Released by Hollywood Pictures/Buena Vista.

Running time: One hour, 53 minutes.

Playing: Citywide.

Our rating: Two Stars.

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Photo

Photo: Bill Cosby plays tutor to Robin Williams' man-childin ``Jack.''