A kid trumps up plenty of reasons to hate his divorced mother and her lover. But "Firstborn" isn't satisfied with that -- it has to tip the balance with a glassine envelope filled with cocaine. Director Michael Apted ("Coal Miner's Daughter") settles for a movie of pat moralism, a pamphleteer's parable of how drugs destroy families.

Which is a shame, because, at its best, "Firstborn" gives us a nightmare vision of what it's like to grow up in a home riven by divorce. Wendy Livingston (Teri Garr) tries to raise two sons, Jake (newcomer Christopher Collet) and Brian (played with bratty wit by Corey Haim), but it's just too hard -- she's lonely, and when her ex-husband decides to remarry, she takes up with a handsome, two-bit drug hustler, Sam (Peter Weller). "We have fun," she says of Sam. "I feel like I've known him all my life. He's full of life, and he needs me."

As in "Valley Girl," the kids want to rebel, but are end-run by authority figures from the generation that made authority a bad word. Screenwriter Ron Koslow gets in some fun '60s-bashing with the dialogue -- when Sam spins out his jejune fantasy of opening a restaurant specializing in mesquite barbecue, he says, "People are waiting to be turned on," and his speech is littered with cliche's: "no sweat," "take it slow," "make it happen." It's counterculture patter the Berlitz way, stylized to sound as it would to a 16-year-old kid who thinks "hip isn't hip anymore."

Apted directs his early scenes in a jazzy, disconnected style -- the framing is almost random, as people cut in and out in front of the camera, and lines of dialogue topple over each other in a chattering frenzy. Cinematographer Ralf Bode has painted the movie with gauzy, ethereal light; this is life as it looks in a nightmare -- fuzzy, exaggerated, chaotic -- Jake's private horror movie as family life dissolves around him.

The actors play along with this conceit. Glassy-eyed, with the thick bones of his cheeks and brow bulging like a Henry Moore sculpture, Weller is one of the most opaque actors around; but here, he's able to make it work for him. Intoning, "Why is everything such a bummer for you, Jake?" in his flat, basso cadences, he's a stoned-out Frankenstein. Similarly, Teri Garr's loopy persona becomes a portrait of a mother any kid would resent. Darting her eyes, hurrying her small voice into incoherences of irritation, she's a moon-faced weakling -- and what else could she be, if Dad left her?

There are wonderful bits by James Harper, as a sadistic teacher who croons, "Boring! Boring! Boring alert!" from the back of the classroom during his students' oral reports, and Richard E. Szlasa as a lacrosse coach who, with play-it-straight pomposity, impresses his charges with the importance of proper post-shower toweling technique ("Head, crotch, feet!" they chant.) As Jake, Collet anchors the nightmare with tousle-haired integrity.

When Jake discovers Sam's stash of forbidden powder under the floorboards, though, the innovative form of "Firstborn" -- the social-realist horror flick -- starts to evaporate, and what is left is just another TV movie about a kid who has to grow up in a hurry because his parents are divorced. The morality of "Firstborn" is TV-conventional: Mothers should be mothers first, drugs are bad. Like "Irreconcilable Differences," "Firstborn" is one of the new Hays Office movies, meant to convince America that Hollywood isn't just a sandbox filled with cocaine. There's an unpleasant smugness to these jeremiads -- cocaine may wreck people's lives, but it's not a complaint most can afford. You don't want to hear it from Hollywood.