ROBERT ALTMAN turns detective movies upside down with The Long Goodbye. It's the latest in a series of films depicting the exploits of Raymond Chandler's fictional gumshoe, Philip Marlowe. Actors from Bogart to James Garner have played him, with Bogart creating the classic rendition. But audiences expecting something in the tradition of The Big Sleep are bound to be disappointed. Altman, the most original and risk-taking of current American directors, creates his own tradition.

Instead of being a nostalgic salute to old Hollywood detective movies, The Long Goodbye tosses the tradition's cliches out the window. Altman waves goodbye to the genre's habit of emphasizing plot instead of characterization. And Elliott Gould, as a Marlowe for the seventies, is like no detective we've ever seen before: a schlemiel forced to live up to his fantasies about justice and derring-do. He is a contemporary Rip Van Winkle, walking around modern-day Los Angeles with ideals and morals from a different era.

The film's complicated story--about a mysterious disappearance and a murder case that turn out to be intertwined--is pretty unimportant. What matters most is the cavalcade of bizarre characters that parade through the movie: a wasted, would-be Hemingway, his mysterious wife, a nonchalant killer, and a sadistic Jewish gangster. The gangster--a shadowy, sinister figure in so many films--is laughably absurd in this movie because he's so exaggerated. His idea of getting down to the bare essentials is stripping down to his dark blue jockey-shorts, so he can talk as a man with nothing to hide.

Altman riddles the movie with moments like this, keeping viewers constantly off balance. He jumps deftly from satire and black comedy to utter seriousness and back again as he introduces new characters. The scenes between Sterling Hayden and Nina van Pallandt (as the drunk, impotent writer and his enigmatic wife) are moving and terrifying. But suddenly, another character enters the picture--one time it's Henry Gibson, playing a creepy little shrink--and the film makes an abrupt, exhilarating shift of gears. Like the rest of the movie, the syrupy musical score can't be taken too seriously. It's the kind of music piped into any dentist's office, or played on any "beautiful music" FM radio station. The theme song turns up everywhere: played on supermarket Muzak, played like a funeral march by a tinny Mexican street band.

ALTHOUGH ALTMAN devotes much of the film's energy to a mockery of the worst excesses of Hollywood melodramas, the heart of the movie is Elliott Gould's portrait of Marlowe. He is the incorruptible core, surrounded by characters who vary only in the degree of their rottenness. Marlowe's may seem to be a naive view of the world, to be sure: His old-fashioned standards are as outdated in today's Los Angeles as his 1948 Lincoln. But the anachronism of Marlowe--the caring man in a Disneyland of indifference--is strangely appealing.

Gould's Marlowe is half-knight and half-clown, struggling against a city's corrupting power. He constantly mumbles to himself to convince himself that he's really a private eye, like someone else would pinch himself to make sure he's not dreaming. Marlowe's Los Angeles is constantly alight with all-night supermarkets, all-night traffic, all-night venality. He is awake to the phonies and moral bankrupts around him, and the audience sees L.A. as he sees it. The restless, light-drenched photography (by Altman veteran Vilmos Zsigmond), and nervy editing and soundtrack express the visual and aural equivalents of Marlowe's discontent and curiosity.

There has been a glut of police and private eye movies in the last few months, almost all of them French Connection ripoffs. But The Long Goodbye stands apart, harking back to an earlier kind of movie where the hero didn't have to abandon his own morality in order to root out others' amorality. Robert Altman has accomplished this without creating a sterile exercise in nostalgia, and has breathed life into the sagging genre of detective films.