Hans J. Morgenthau, 76, a leading foreign policy scholar who was one of the first and most prominent opponents of the Vietnam war, died Saturday at Lenox Hill Hospital in New York.

During the period of the teach-ins that sprang up on campuses across the nation as the war began to escalate in 1965 and 1966, Mr. Morgenthau became known as one of the most forceful and vehement of those who spoke out against the conflict.

If the academic world helped focus the nation's opposition to the war, Mr. Morgenthau was perhaps foremost among those who crystallized early antiwar sentiment within academia. Vigorous and often contentious, the debate thrust him into the public eye, surrounded him with controversy and provided renown far beyond what he had earned already with his somberly philosophical studies of American foreign policy.

Mr. Morgenthau, a German Jew who left his native country after the rise of Adolf Hitler, was a professor at the University of Chicago at the time of the Vietnam war.

From 1974 until recently he taught at the New School for Social Research in New York. His death Saturday followed a brief illness.

Many of the new formulations of American foreign policy that have been gaining attention and adherents in recent years may be seen to conform to the theories and doctrines propounded by Mr. Morgenthau.

In a 1969 book, titled "A New Foreign Policy for the United States," Mr. Morgenthau called on Americans to "free ourselves from the burden of obsolescent policies which have become mechanical routines . . . ."

These policies, he argued, were the ones formed in 1947 to combat the menacing challenge to the West that was then posed by communism, and were no longer valid.

Present-day rejection of a United States role as "policeman for the world" may be seen as a logical consequence of the foreign policy formulations put forward by Mr. Morgenthau.

It was his belief that the policies devised for the post-World War II world and successful at that time had even become dangerous in the 1970s.

For example, he contended, there was no reason to believe that merely because foreign aid had stemmed the spread of communism in Western Europe it would automatically have the same result in Southeast Asia.

He was concerned by what appeared to him to be the unthinking desire to export either "the American Way of Life" in general or the "Great Society" in particular to all parts of the world.

Neither was he willing to accept blindly the concept of collective security that had become so firmly rooted at the foundation of American foreign policy. t

What he called for in his book was a "radical rethinking of the issues and of the policies adequate to them."

Critics -- and they were numerous -- were put off by what some of them saw as an almost despairing realism that Mr. Morgenthau appeared to offer as the basis of foreign policy.

Indeed, it is clearly possible to view Mr. Morgenthau as one of those who, well before the Vietnam war, began to introduce the nation to a pessimistic sense of the limits of its ability to influence world events.

In a nation once buoyed with an optimistic vision of its own powers, Mr. Morgenthau was one of those who helped in arousing a sense of the bewildering complexity and ultimate intractability of many foreign policy problems.

A man who called for unemotional, pragmatic analysis of the national interest, Mr. Morgenthau was known particularly in the Cold War years of the 1950s as a champion of military preparedness, yet one who shunned the crusading spirit as a motive for policy.

"The anticommunist crusade as an instrument of foreign policy is likely to destroy all nations, communist and anticommunist alike," he wrote more than two decades ago.

In keeping with his stance as realist, he also criticized what he considered an excessive American solicitude for world opinion.

"This world opinion we pay so much attention to is largely a myth," he was quoted as saying. "Our position should simply be to think and act in terms of our own self-interest. If so-called world opinion supports our self-interest, well, that's fine. But if it doesn't . . . we should ignore it."

From its earliest days, Mr. Morgenthau did not appear to find the Vietnam war and the way it was waged consistent with the self-interest of the United States as he saw it.

In explaining the justification for his opposition, he once cited "Politics Among Nations," a book he published in 1948.

"Never put yourself in a position from which you cannot retreat without losing face, and from which you cannot advance without great risks," he wrote.

Mr. Morgenthau, the son of a physician, studied history, law, economics and philosophy at the universities of Berlin, Frankfurt and Munich, and was for a time a practicing lawyer n Germany.

While teaching law and studying in Switzerland in 1933 he decided not to return to Hitler's Germany, and in 1937 came to the United States. In addition to teaching at Chicago and other prominent universities, he was admitted to the bar in Missouri in 1943.

In recent years Mr. Morgenthau voiced strong criticism of the CIA. He wrote in 1974 that "With unfailing consistency we have since the end of the Second World War intervened on behalf of conservative and fascist repression against revolution and radical reform . . . such a policy can only lead to moral and political disaster."

Survivors include a son, Matthew, and a daughter, Susanna.