Hans Morgenthau has never been lost in an ivory tower. A foreign policy expert from the University of Chicago, he promises to rid his 175 Summer School students of their "favorite illusions" before the close of the term. Morgenthau, himself, is a professional realist who finds idealism very expensive.

His mission is to alter the thinking on foreign policy so that a realistic negotiated settlement will be possible with Russia. He is tired of the United States embarking on policies that are impossible to carry out.

"The refusal to negotiate in the false conviction that conflicting interests are irreconcilable is to court a needless war." So Morgenthau would divide the world into a Russian sphere of influence and an American sphere which would "make possible a long era of peace."

In lecturing on foreign policy, he describes it as the quest for power or the maintenance of power. The United Nations, to him, is merely a new instrument for the exercise of power politics.

Morgenthau's early years may help to explain his views which have led some to think of him as a "wicked preacher of international immorality." Born in Germany (he looks older than 47), he received his education there and started a legal career there. But he left Germany in 1932 and taught for a time in Switzerland and Spain.

Coming to the United States in 1937, he managed to get a job at Brooklyn College while his wife sold hats at Macy's. In addition to teaching, he learned enough American law to be admitted to the bar and try one case. ("It was a good brief, but we lost.") He came to the University of Chicago in 1943 and became nationally known in 1948 with his book, "Politics Among Nations."

Lecturing without notes, Morgenthau gets very absorbed with his topic but the slightest disturbance may threw off his thinking. He stopped a student from standing in the back of Sever 11 because "it makes me think you are just passing through." Morgenthau has been waging a no-decision contest with a Lowell Institute microphone all summer as one of his two Government courses is recorded for rebroadcast next winter.

Much of his class time is devoted to answering students' questions, and Morgenthau is at his best defending himself against criticism. ("It's Russian imperialism that we have to be worried about. Some speak of an inevitable ideological war, but don't take Soviet writings too seriously. Remember the only thing that has withered away in Russia is the opposition.")

During his career Morgenthau has been occasionally confused with the former Secretary of the Treasury Henry Morgenthau who is no relation. The latter formulated the "Morgenthau Plan" which would have turned Germany into an agricultural country.

"When I was announced as a lecturer in Europe," the professor reports, "people used to call up local American officials to make sure I hadn't written 'The Plan.'

"The Morgenthau Plan contained one sound idea; we had to take away Germany's ability to make war rather than to try to change their minds. Even today in Germany the spirit of democracy is significant by its absence. Those who opposed Hitler talk like the Nazis without knowing it.

"The mood of the democratic minority is one of despair. They say they cannot stay when the occupation forces leave. People show no deep loyalty to the West German republic, just as people locally would not die for the Boston municipal government."

Morgenthau directs his most bitter criticism to appeasement on the home front. "Sometimes Mr. Acheson acts as a great statesman, and sometimes he acts as a member of the Truman administration. Appeasing MacCarthyism domestically does not pay anymore than foreign appeasement does. Acheson operates under political obstacles and does things he can't approve of intellectually. The administration underestimates the people and fails to take them in its confidence."

Americans are under a great many sentimental illusions, according to Morgenthau. The United States interfered in Korea because it was in our national interest to do so, and it was not really United Nations collective action. "Some of the other countries sent nurses to Korea, perhaps to show the boys what they are fighting for."

Unpleasant as some of Morgenthau's views seem, he is on the side of peace and live-and-let-live, for "war has ceased to be a rational way of settling disputes." "It is a lesser evil for the Lathuanians to be enslaved than for everyone to go to war over their fate. No foreign policy can make everyone happy.