APOCALYPSE NOW -- In 70-mm and six-track Dolby stereo at the Uptown. Additional engagements, in 35mm, start Wednesday at the Annandale and Beltway Plaza.

Some years ago, it used to be said that Vietnam wasn't movie material, as that simple historical episode called World War II was. The good guy-bad guy situation was too ambiguous to be filmed, critical wisdom had it, leaving little doubt that events, not movie-making, were to blame for this misfortune.

But some people can't resist a challenge. After a few "small" movies in or around wartime Vietnam, the blockbusters started, and now, after more time, money and toll on workers' health and marriages (details at your supermarket newsstand) than any previous venture, come "Apocalypse Now," described by its creator, Francis Ford Coppola, as "a theatrical-film-myth dealing with the theme of moral ambiguity."

The title and the description give fair warning that the problem of complexity has been solved: One deals with moral ambiguity by showing that it's complex.

The strange thing is that this preposterously named and ballyhooed film does this, stunningly, for nearly two hours. After that, it gets bogged down in the most gaudily festooned moral mishmash you ever saw.

The major part of the film shows a young, dutiful and war-engrossed captain painfully making his way on a rickety patrol boat up river to Cambodia, where he is to "terminate with extreme prejudice" a once-brilliant American colonel said to have gone bonkers. Captain Willard, in Martin Sheen's portrayal, is the perfect instrument for moral struggle, calmly sensitive and open-minded. As he studies the dossier of his intended victim, he recognizes the problem of even talking about "murder" and "insanity" -- "charging a man with murder around here was like handing out speeding tickets at the Indianapolis 500" -- let alone judging how a war should be conducted.

But this is not a war-is-evil pronouncement. Willard is trying to decide what reasonable wartime behavior is, and the incidents along the river keep adding illustrations of the problem. At one time, his young boat crew -- "rock'n'rollers with one foot in the grave" -- gun down a civilian boatload they mistake for smugglers. When it's apparent that they failed to kill one woman, these young Americans naturally want to do the humane thing and take her to a hospital, delaying the mission and endangering themselves. Willard sees the irony of this policy to "cut them in half with a machine gun and give them a Band-Aid" and, to the others' horror, finishes her with a bullet.

Another episode involves Robert Duvall as an American officer who takes a spirited, imaginative and therefore utterly crazy approach to his job -- surfing in just-taken waters, or "spooking" a village by broadcasting the Valkyries' theme from bombers -- for which his men adore him.

And so on, up the river, until Willard reaches the Cambodian village where his Colonel Kurtz is the absolute ruler. Here's where some moral ambiguity is badly needed. Everything Willard has read about Kurtz has led us to believe that he will be a man who has had some profound philosophical collision, from which important questions, at the least, will be revealed.

But darned if it isn't Marlon Brando, shaved bald, but otherwise playing the pretentious role he played as Superman's father before that film turned good. That's two short, notoriously expensive roles, little better than "guest appearances," in which that respected actor's part has dampened an otherwise good picture.

Kurtz lolls on crude thrones, hardly visible in flickery torchlight, his kingdom strewn with fresh corpses. We see by his bedside table that he's reading "The Golden Bough." He talks of "horror" a lot, but as he also contributes to horror -- e.g. , dumping a newly butchered human head on Willard's lap -- it's hard to see what he stands for. Was all that physically and psychologically taxing journey for the purpose of seeking the wit and wisdom of Jim Jones?

So it seems. The mighty wrestling match with "moral ambiguity" is over. This is a bad guy. How or why he turned bad, we don't know, but cult-killing is clearly worse than warfare, and our hero's duty is clear.

And so it is that, after all, the "small" statements, the difficult dilemmas suggested by concrete incidents, turn out to be more important than the grand, sweeping attempt to wrap up the meaning of such complexity as Vietnam.