"Le Samourai," opening today at the Key, is a small diamond cut with terrible precision: cool, elegant, dazzling and totally individual.

It treats crime like Noh drama and criminals like tired knights, the samurai of the modern age, overflowing with their own kinds of honor, loyalty and stoicism. It is a fatalistic, highly stylized vision, romantic in its own way - the firm opens with a title reading "There is no greater solitude than that of the samourai, unless perhaps it be that of the tiger in the jungle" - but as executed by director Jean-Pierre Melville, it is enviably effective.

Melville, who died in 1973, was mad about all things American, even to the point of changing his last name. The French New Wave directors considered him a kind of spiritual father, and he is kind of spiritual father, and he is best known to American audiences for playing the filmmaker Jean Scberg interviews in "Breathless" who tells her his aim in life is "to become immortal and die."

As a director, Melville was fascinated by American gangsters movies of the dark, amoral, fatalistic film-noir variety. He reworked them in line with his own existential leanings, turning out cerebrally sinister films, peopled by enigmatic loners who were given to saying things like, "All men are guilty. They're born innocent, but it deesn't last."

Melville's death and the resulting confusion over the owned the rights to his films has meant that few of them - "Doulos, the Finger Man," starring Jean-Paul Belmondo, and "The Red Cirle" are two - have reached the United States.

"Le Samourai," completed in 1967 and one of the best, has had a sad history. Released here in 1972 in a badly chopped-up, dubbed version idiotically retitled "The Godson," it is being shown at the Key in the only complete, subtitled version currently available, whcih is unfortunately a slightly faded 16mm print. Yet even in this non-pristine form, it really should not be missed.

The samourai of the title is Jef Costello, a Parisian hired killer who lives in an unrelievedly bare room with only a small bird to keep him company. His meticulously planned murder of a nightclub owner starts to unravel, however, as the inspector continues to suspect him despite a perfect alibi. Hunted by both sides, Costello must find a way out.

Playing Costello, and on screen for almost the entire film, is Alain Delon, who in all the time nven. Trenchcaoted, cigarette dangling ominously from his lips, he is lean, implacable, totally emotionless, a Buster Keaton of crime. Breathing heavily after a long run passes for a serious crisis where he is concerned.

"Le Samourai" avoids dialogue as much as possible, and its pared-down look - as well as Melville's concern with honor and fate, his feeling for pure ritual - serve only to screw the tension level even higher. In fact the film's stylized nature means that its occasional burst of violence, bloodless though they are, puncture the surface with a shcok value that messier scenes in other films can't equal.

An austere poem of crime, "Le Samourai" manages to have a grip of an old-fashioned potboiler as well. Not a half-bad combination.