"When it comes to what cops are really like, the movies haven't got a clue," says James Garner in the growly voice-over to "The Glitter Dome," a perversely stylish HBO movie that premieres on the pay TV service tomorrow night at 8. Whether the film, adapted from a Joseph Wambaugh novel, knows what cops are really like or not, it's a high-impact production, well beyond HBO's average.

You could hate it, but you couldn't write it off. As a microcosm of a microcosm, a portrait of Los Angeles de los Sleazos, "Glitter Dome" -- named for a bar in which the cops have their consoling drinks -- is certainly more seedily evocative than Brian DePalma's "Body Double," and there's plenty of tawdry stuff going on in it, too. The murder of a studio executive leads police detectives played by Garner and John Lithgow into realms of prostitution, kiddy porn, mutilation, dope dealing and various denominations of twilight-zone sexuality.

Adapter Stanley Kallis occasionally walks into a wall when he tries to modulate from sick comedy to urban shockeroo, but the performers help disguise the unseem- ly seams -- Garner particularly, though he's required to be a little too sour, and in the first half-hour, his world-weariness seems more weary than worldly. Nobody else, however, could give just the right bitter snap to lines like "Halloween in Hollywood is redundant" and "There is no gravity; the earth sucks." Garner is like a male Eve Arden, a totally singular sardonic voice.

Lithgow plays his partner, recently unnerved by a divorce and by an atrocity encountered on assignment that keeps recurring in ghastly flashback. Unfortunately, the pair seems a little low on team consciousness, at least as compared with some of the cemented duos of "Hill Street Blues," whether those depictions are authentic or not. But then both Lithgow and Garner are upstaged in many scenes by visitations from the electric kitten Margot Kidder, who is wickedly provocative as a coke-snorting actress who knew Mr. Big before he got blammed to bits in the back seat of a silver Rolls.

At a naughty Hollywood party, Kidder, as "Willie," gets carried away and coaxes cop Garner into the greenhouse. There she delivers a tantalizing, scandalous verbal directive: "Get your handcuffs out." Fortunately the scene goes comic rather than kink-erotic, Margot now bound and writhing and babbling "I'm helpless, you filthy gorilla; I can't stop you!" In time the couple will share a less bizarro assignation. Kidder is a magnificent tease; this performance is full of mocking, netherly reverberations.

For a film to go from grotesque comedy to grotesque tragedy without seeming schizzy would require a very deft director. Stuart Margolin, Garner's old "Rockford" pal, is not that, and in this production he has overextended himself besides. He directs, he plays the limp-ankled nephew of the slain executive, he wrote the banal music (including a main theme that is so close to "Lover Man" they should have just bought the rights to use "Lover Man"), he coproduced. Too much. His directorial style is a jangle of clashing approaches; for every one that demonstrates deadly aim, there's a corresponding misfire.

But that doesn't undermine the picture entirely, and in the real clinches, even Margolin tends to come through. A highly qualified supporting cast includes the late John Marley, required to do too much mindless barking as the police captain, and Colleen Dewhurst, who justifies her presence -- in the role of an aging, raspy lesbian who has taken in a 15-year-old girlfriend -- with the flawless delivery of one delightfully unprintable line (if "Glitter Dome" were submitted to the Motion Picture Association's review board, it would get an R for language alone).

However faithful the film is to the book, one is left with that haunting, distinctly Wambaughian tingle when, after many unsavory slices of unsavory lives, it's all over. "You'd think this is a cop story," says Garner in the opening narration. "It's not. It's a story about survival -- mine." And perhaps about even more than that. In a TV season that has every network bragging that its shows "sizzle," this HBO movie really does.