For more than a decade, it has not been the "in" thing to talk about Vietnam.

Despite its huge toll in American lives, the Vietnam war has not over the years been romanticized on film and in books as with World War II, or even Korea.It has been exorcised from an American national psyche that likes its history untrammeled and uncomplicated. Vietnam's veterans have often been treated shamefully by a country noted for its generosity. Perhaps all this is because it was a war, in the end, without popular support; a war of horrible excesses like the massacre at My Lai; a war Americans did not win.

But things are changing, and with movies like "Platoon," and books like Neil Sheehan's "A Bright Shining Lie," there is a new willingness to confront Vietnam and learn from our anguish.

Let us hope Americans do not again have to fight in far-off places against guerrillas steeped in the concept of revolutionary warfare. But if they do, let us hope that the politicians and military commanders who direct that war will have learned the lessons of Vietnam.

They should read Mr. Sheehan's new book, which is at once a history of the Vietnam war and a biography of John Paul Vann, one of the most remarkable Americans to have served there.

Mr. Vann was a smart, scrappy lieutenant colonel who rose from tragic circumstances (the illegitimate son of an alcoholic, part-time prostitute) to find respectability and purpose in the American Army. There was a dark side to his personal life. He was sexually voracious, ran out on his wife, and even played off Vietnamese mistress against Vietnamese mistress.

But as a soldier he was courageous and noble. His enemies were the Viet Cong and North Vietnamese; he deplored and raged against senseless cruelty to civilians. He strongly supported the war, but was stridently critical of the manner in which it was waged both by the United States military and the Vietnamese.

He contemptuously dismissed the orthodoxy of U.S. generals against guerrilla fighters, as well as the indiscriminate use of air power and artillery. He believed that the key to successful counter-revolutionary warfare was not to terrorize the civilian populace but to win their support and assure them of security against the communist guerrillas. His outspokenness, and his channeling of his views to the press, got him in trouble with his military superiors. He resigned from the Army but returned to Vietnam as a civilian official, ironically with sweeping authority even over American military forces. He eventually died in a helicopter crash.

Was it a just war? Were American tactics inept? One must seek the answer to these questions not only in the past but also in the present.

On the one hand, today's men of Hanoi smilingly court diplomatic relations and U.S. aid to rebuild their shattered country. But on the other hand, thousands of refugees still set sail for terrible privation in leaky boats at sea rather than live under their rule.

Thousands of miles away in Washington, the names of American dead march endlessly across the black granite of the Vietnam war memorial.

The plight of today's refugees suggests that the American soldiers did not die for a dishonorable cause.

The lesson of Vietnam may be that they died for an honorable cause, but fought, at times, less than honorably.