People of the United States must let these behind the Iron Curtain know that this country would use the atomic bomb only for retaliation, Senator Ralph E. Flanders said last night in Littauer auditorium in this fall's third and final Godkin Lecture.

In contrast with his first lecture, in which he stressed the problem of an American depression as being more serious than the threat of a Russian attack, the Republican junior senator from Vermont emphasized the atom bomb as a preserver of peace, although he insisted that it should not be used "against conquered and enslaved populations."

While urging that the people behind the curtain be informed that the United States will not use the bomb unless forced to do so, Flanders asserted that "they must be ready for bombing which destroys their war industries and transportation."

Flanders stressed the importance of a strong air force but insisted that it would be a grave error for this nation to engage the Soviets in an armament race. Such a venture would be a "costly and destructive defensive operation."

The senator argued that the only alternative to strong armament lies in getting across the truth about United States intentions to the Russian people.

Flanders suggested the possibility of dropping propaganda leaflets through the air. "A nation like ours, which resigned itself to, and practiced the mass murder of civilians by aerial bombing in the last years of the war, need not be fussily hesitant about trying something new in the interests of peace."

"The nation which dropped on the citizens of Japan the devastating atomic bomb makes itself ridiculous when it hesitates at any means of assuring the peoples under the yoke of our potential enemies that we have no quarrel with them."

The title of last night's lecture was "Pax Americana."