FOR those old enough to remember the sight of helicopters airlifting the last few Americans out of Saigon as the city fell to the North Vietnamese, two decades is still too short a historical lens with which to view the Vietnam War clearly.
The 20th anniversary of the fall of the South Vietnamese capital, to be marked this Sunday, together with a new book by former Secretary of Defense Robert S. McNamara in which he confesses that US foreign policy in Vietnam in the 1960s was ''terribly wrong,'' has reignited a testy national debate over the war. We have learned that time has not yet brought consensus; at best, Americans have uneasily ''agreed to disagree'' about the war and about what alternative policies might have yielded.
Some continue strongly to believe, as Mr. McNamara strongly does not, that a more unified and fully committed US effort could have brought military victory. Others anguish that thousands of American lives (and millions of Vietnamese) were lost unnecessarily through US involvement in a far-off civil war that posed no threat of a Communist advance throughout Asia.
Today, Vietnam is a backward country of 72 million people eager to lure investors from the United States. Many Asian nations, led by the South Koreans, are already there in force. As one American businessman put it, ''There will be many opportunities here... . They need everything.''
A 19-year US trade embargo on Vietnam has been lifted. And Vietnam would like to establish full diplomatic relations with the US. By all accounts, it is marking its 1975 victory circumspectly, celebrating ''national unification'' without hostility toward America. Human rights abuses continue, in particular against Buddhist monks, but the government has made measurable progress. And it is cooperating in the search for 1,621 Americans still missing in action in Vietnam, an effort it realizes must continue if diplomatic recognition is to be granted.
In the US today, younger Americans are not transfixed by the Vietnam War. For them, it is a historical artifact. They don't carry the emotional baggage of their parents and grandparents. That is largely good.
We are only five years from a new millennium. There is an American future to be carved out. We must take seriously McNamara's advice and learn the lessons of Vietnam. Then we must apply them to the tasks of today.