Sen. Eugene J. McCarthy (D-Minn.) gave his third and final William Belden Noble Lecture last night and finaly discussed the issue his audience had been waiting for -- the war in Vietnam.

Before an audience of more than 300 people in Memorial Church McCarthy condemned the war and said that it threatened to dehumanize and decivilize the American people.

In the First and Second World Wars our actions were justified, McCarthy said, since we were helping to preserve Western democracy from possible destruction. But he added in the present war, we have lost the support of the decent opinion of mankind which we enjoyed in both of the previous major wars.

Kill Ratio

In a restrained and unvitriolic manner McCarthy discussed some of the moral issues involved in the war. He objected especially to the high ratio of civilian to military casualties in Vietnam. This is due partly to the new weapons we are using and partly to the new ways we are using old weapons, McCarthy said.

McCarthy stressed that he does not advocate an immediate and complete withdrawal of all American troops which, he said, would be impractical. Instead, he supported a limited withdrawal into well-fortified bases along the lines of the enclave plan which General Gavin suggested to the Senate Foreign Relations Committee last year.

No Devastation

This plan, McCarthy explained, would be an alternative to an effort to completely conquer and devastate South Vietnam. While we are still in a position of strength, the United Nations or some other international group could work toward a peace settlement, McCarthy said.

Progress in this war, McCarthy said, is measured in terms of kill ratios and numbers of casualties. He said that the enclave policy would make possible a return to the traditional type of warfare, war for territory and position.