REVIEW

LEAD: The New Directors/New Films festival is presenting a number of unconventional documentaries, but none as alarming and significantly lunatic as ''The Emperor's Naked Army Marches On,'' conceived by Shohei Imamura (''Vengeance Is Mine'') and directed by Kazuo Hara as his first feature. The New Directors/New Films festival is presenting a number of unconventional documentaries, but none as alarming and significantly lunatic as ''The Emperor's Naked Army Marches On,'' conceived by Shohei Imamura (''Vengeance Is Mine'') and directed by Kazuo Hara as his first feature. Its central figure is Kenzo Okuzaki, 65 years old, a World War II veteran who lives in Kobe with his pliant, uncomplaining wife, whom we later learn is dying of cancer. At the start of the film, Kenzo has already spent 13 years 9 months in jail. His crimes: plotting to assassinate a former Prime Minister, attempting to hit the Emperor with lead pellets fired with a sling shot and distributing pornographic pictures of the Emperor to people outside a Tokyo department store. Kenzo is a political activist. He's also a marriage broker. In an astonishing and funny precredit sequence, we see him delivering a wedding feast homily in which he recalls his years in jail and suggests that all countries and, indeed, all families are barriers to the true brotherhood of man. The bride and groom listen with eyes lowered, as if this were the sort of thing every bride and groom expected to hear on their wedding day. ''The Emperor's Naked Army Marches On'' will be shown at the Museum of Modern Art at 8:30 tonight and 6 P.M. tomorrow. From everything the audience sees, Kenzo Okuzaki is a certifiable psychotic, though ''The Emperor's Naked Army Marches On'' never addresses this suspicion. He's the sort of fellow who writes long, crazily incoherent letters to editors, confronts people on street corners and harangues them with a loudspeaker from his van. It could be that Mr. Hara thinks the psychotic state is the only sane response to the contradictions in contemporary Japanese society. Whatever the film director thinks, he never says. Instead he follows Kenzo around Japan as the former soldier tries to get at the truth of something that happened more than 40 years ago - the execution of three of his army comrades when they were serving in New Guinea at the end of the war. The audience never understands just why, at this late date, Kenzo decides to investigate these events, the details of which remain fuzzy. With Mr. Hara and a camera crew in tow, Kenzo calls on former officers and enlisted men he thinks were responsible for ordering the executions. There are suggestions that the men were condemned for desertion or for cannibalism. There's the further suggestion that they were executed to provide meat for their starving comrades. Some of those interviewed treat Kenzo with respect and attempt to answer his questions. Others equivocate. Some contradict themselves. Through all the testimony, Kenzo behaves as if he had been appointed by God to act as His prosecuting attorney. At one point he starts beating an old man who is sick, while the old man's wife pleads: ''No violence. No violence.'' The farce becomes dark and disorienting. The cops are frequently called, and Kenzo often has to admit that there are some circumstances in which violence is called for. He says it with the stoicism of the true fanatic. At one point he decides he'd like to have his own jail cell in his house and drives off to the Kobe prison to get the measurements. When he's not allowed in, he goes into a tirade about the guards being ''law's slaves, just like the Emperor.'' It's difficult to understand ''The Emperor's Naked Army Marches On'' without knowing more of the facts than the film wants to give. It may be that there really are no more facts. What we see is all there is. In that case, the film raises pertinent questions about the extent to which the presence of the camera ''entraps'' events that otherwise would never have occurred. In some documentaries, like this one, the questions are especially pertinent. The most invigorating thing about ''The Emperor's Naked Army Marches On'' is its consistent irreverence. It doesn't mean to be polite or nice or soothing. It means to provoke and disturb - and let the devil take the hindmost. A screen note at the end ot the film reports that after photography was completed, Kenzo set out to assassinate one of his former Army comrades and, unable to get at him, shot and wounded the man's son instead. He is now serving a 12-year prison sentence, seeming to be very happy, as well as satisfied that his wife died earlier than expected. Otherwise he would have had to worry about how to take care of her. MORE QUESTIONS THAN ANSWERS - THE EMPEROR'S NAKED ARMY MARCHES ON-directed by Kazuo Hara; in Japanese with English subtitles; photography by Mr. Hara; edited by Jun Nabeshima; produced by Sachiko Kobayashi; production company, Shisso Production, Tokyo. At Roy and Niuta Titus Theater 1, Museum of Modern Art, 11 West 53d Street, as part of the New Directors/ New Films festival. Running time: 122 minutes. This film has no rating. WITH: Kenzo Okuzaki