IT OCCURS SOMETIME during the 1860's, just after the samurai warrior class has lost its privileged position in Japanese society. As the credits cease rolling, the camera focuses on an unshaven samurai (Toshiro Mifune) standing alone in the middle of a crossroads. He dispassionately scratches his back then tosses his walking stick. And, without a backward glance he follows the road it indicates.

So begins Yojimbo plot source of A Fistful of Dollars and one of the world's classic "westerns." It's a Japanese movie but contains many elements familiar to the fan of the American horse opera. There is the wandering, homeless hero, the isolated town being destroyed by rival factions, a beautiful woman in distress and finally, a showdown--Japanese style. However, Yojimbo goes beyond all this and so avoids the mediocrity of a morass of cliches. Akira Kurosawa, the director, who focused world attention on Japanese cinema with Rashoman and Seven Samurai, succeeds in Yojimbo without resorting to either didacticism or melodrama. Violence accompanies comedy and through this incongruity. Kurosawa states that even in its evilest moments, the human animal is funny. Perhaps, Kurosawa believes that only then is man funny, for in the film, when the evil is vanquished, so is the humor and nothing remains.

Except for Mifune's role, the characters are either totally good, or totally bad. This is a necessary simplicity because in the god-like justice the samurai metes out, there can be no hesitation, no doubts about his way's being best, no room for speculation about possible reformation.

THE RIVAL FACTIONS are equally immoral and led by men of ordinary appearance: a silk merchant (Kamatari Fujiwara) and a sake merchant (Takashi Simura). These men manipulate groups of extraordinarily conceived caracatures of evil. The degeneracy of the merchants is hidden beneath masks of respectibility and only when they make their plans is the full measure of their malevolence revealed. With their henchmen, however, the situation is different. They boldly flaunt their fugitive status and are terrifyingly eager to implement the merchant's plans for destruction. A henchman (Tatsuys Nakadai) of the sake merchant epitomizes the hyperbole. The only person in the town who owns a pistol, he takes complete advantage of the fact. With obvious pleasure he flourishes the tool and when he kills with it, observes the death with cruel joy. At film's end, in typical badman style, he pleads to be allowed to die holding his gun and after his request has been granted, expires while struggling to kill the samurai.

The range of Nakadai's emotions nearly breaks the rigidity of his role. One can deduce that the part only called for the characterization of a gun-happy youth, but he extends it to include the henchman's realization of the role firearms will have in Japan's future.

Only the samurai fully understands the town and he sets out to destroy the bad-guys. However, this attempt is not sparked by altruism. Instead, the catalysts are boredom and the possible opportunity for reward. With characteristic disinterest, the samurai maneuvers the factions into warfare, then sits stop a watchtower and on looks with the unconcealed glee of a tomcat observing a goldfish bowl. But his efforts are thwarted so the warrior must renew his plans.

Feigning degeneracy equal to the factions', the samurai succeeds in provoking another war, but lapses into compassion and rescues a farmer's abducted wife. For the first time, he directly involves himself in the action. As a result, he incurs the wrath of both rival groups who try to kill him and only through the aid of the coffinmaker is our hero rescued. Several days later he has recuperated enough to confront the survivors of the war. With the watchtower in the background, the shot shows the warrior gazing down a dust-blown street at his opponents. They are ten strong: he is one man. Then, as the dust swirls around the samurai's head, he smiles. He has accepted his mere humaness and he will triumph.

The picture is totally Mifune's but this is due more to Kurosawa's expertise than the actor's, since Mifune tends to rely upon a fairly predictable set of movements no matter what role he plays. He can always be expected to use a toothpick as a prop, to scratch upon occasion and to walk with the same gait. In the cutting room and on the set Kurosawa transformed these actions into a portrait of a pensive, slightly down-and-out, but still powerful samurai.

MUCH OF THE HUMOR in Yojimbo is based on Kurosawa's sense of irony. For instance, when the samurai enters the town, the first sight that greets him is of a small dog. Rinky-dink music accompanies the dog as he trots towards the foreground. Finally, the animal is in perfect focus and one can discern that in its mouth is--a human hand.

The warrior's perception of reality reduces any scene to its proper dimensions. When the silk merchant makes an attempt to woo him through the use of dancing girls, the camera focuses on the dancers' insipid expressions and stylized foot motions while the sound track conveys their uninspired attempts at music-making. Then, there is a close-up of the samurai's face stamped with a look of such marvelous scorn that the dancers become a spectacle of banality.

The end of Yojimbo offers no humor. The bad-guys are dead and no room is left for irony. Only the good townspeople, the samurai and the constant dust-laden winds remain.

Clint Eastwood and the spaghetti westerns never had it so good.