According veterans their due

THEY were two totally different wars, World War II and the Vietnam war, and the American public's reaction to them was equally disparate. The earlier conflict was popular, its purpose clear, its result victory. The later one was unpopular, its purpose obscure, its result inconclusive.

Yet the reactions of Americans toward veterans of both wars ought to be the same: great appreciation for their having served their country, at personal risk. Until recently this was not the case. Veterans of World War II (and most other conflicts) were honored. But too often those who had served in Vietnam were not, made instead to feel personally responsible for their government's controversial decisions about the war.

Finally this is changing, 11 years after American forces pulled out of Vietnam. In recent months the Vietnam veteran has begun to be accorded the respect and thanks that have always been his due. Parades have been marched and speeches given; a moving memorial has been erected in Washington.

And this past weekend special nationwide attention focused on honoring the unknown serviceman from Vietnam, in a way that honored all veterans of that contest. As President Reagan said in one of the most moving addresses of his presidency: ''Let us, if we must, debate the lessons learned at some other time . . .'' - there is a time to think of the veterans who serve.

Two events, nearly back to back, put the focus there. One is the weekend attention on the Vietnam unknown. The other is the 40th anniversary of D-Day, June 6, when the largest invasion force in history gained a toehold on Hitler's Europe under horrendous conditions and, through the efforts of thousands of servicemen, began the then-inexorable process of liberating a continent from tyranny.

Today veterans of that invasion are again in the national spotlight as they trek back to the beaches of Normandy, viewing the scene in peace and remembering the purpose of that war. In the intervening decades these veterans have been treated with respect and honor. A grateful government has met many of their needs.

It is time to do equally well by veterans of the Vietnam war: They deserve no less.