"Cocaine: One Man's Seduction," on "NBC Sunday Night at the Movies," grippingly tells the story of a 47-year-old man who goes from the end of one rope to the end of another, except that the other rope is on fire.

The filmmakers and actors involved in this superior production, airing at 9 tomorrow night on Channel 4, gave it their all, and the results are as shattering as they were intended to be.

Dennis Weaver plays the "one man" of the title, a real estate agent in San Diego whose dreams of upward mobility have suddenly hit a snag; for 10 years he was the top salesman, but now he has slipped down the sales chart, and he is possessed by the mortality panic that only the middle-aged can know. "Time's not on my side," he says with agonized precision. At a party, a girl offers the one-word invitation, "Toot?" and before long, the man graduates from casual user to certifiable addict.

While the drug energizes him, revitalizes his career and helps give him the confidence to play in a more rarefied league of his ruthlessly competitive business, it is also dragging him into the slavery of dependence and physical abuse. "Cocaine" may sound like a sermon--and it is, justifiably so--but it doesn't play preachy, largely because Dennis Weaver is a television actor of intensely powerful credibility, and one who, for the most part, saves himself for roles that deserve him.

This one does, and his study of "one man's" descent works simultaneously as the portrait of a real person and as a chillingly representative case study in addiction. First-rate support is given him by Karen Grassle as his wife, who doesn't recognize the symptoms until they reach a life-or-death stage, and James Spader, who seems to be getting all the troubled teen-ager roles these days, as their 18-year-old son Buddy. He discovers his father's habit and finds himself involved in a daunting case of role reversal.

Even dramas that depict the nightmare potentials of a drug like cocaine--or alcohol, or whatever--risk the danger of glamorizing the drug. This doesn't really happen in "Cocaine," which can take its place alongside outstanding addiction movies of the past, from "Lost Weekend" to "The Man With the Golden Arm." The film was produced with an obvious message in mind--it's utility filmmaking, nothing arty--but writer Barry Schneider and director Paul Wendkos, always a sure hand, make the story and characters real, not just figures in the TV equivalent of an army training film.

The middle-class lives are made complete by tellingly observed details. Everything is frighteningly right, and that helps make Weaver's disintegration that much more traumatic to all concerned. He has his first hit in a bathroom at a posh party; suddenly the wallflower afraid to mingle is the life of the affair. Career and social pressures are depicted with stinging economy, and Wendkos, not one to waste motion, keeps Weaver in merciless sharp focus throughout; he is a victim not just of circumstances, but of his own character weaknesses. Running on high, he buys a new Seville, and as he drives it home, Wendkos shoots him from a speeding helicopter to emphasize the false exhilaration that will soon enough take its toll.

Jeffrey Tambor, as a friend of Weaver's, gives what may be the best performance of his career. He's the card-playing buddy who excuses himself to the bathroom a bit too often, but it isn't learned until later that his devotion to cocaine has reached religious proportions. The symptoms displayed by Weaver's character are classic--"I'm not into it that heavy," he keeps saying, even as his dealer claims not to be a dealer--but they are so skillfully portrayed that even the viewing "happy" cocaine user, inclined, of course, to scoff, might be given pause.

Is the problem depicted really a national problem, or just a southern California problem? The question may be moot; southern California has a way of writing the problem manifest for the rest of the country, even as it holds out its spiffy and trim new version of the American dream. One of the enviable things about "Cocaine" makes this consideration beside the point, anyway; it works as drama, the kind of drama that makes one grateful for being grabbed by the lapels and shaken but good.