Intellectuals must assume a more active role, if the United States is to counter the Communist "challenge to all our fundamental values," William A. Sullivan, Assistant Director of the FBI, stated yesterday.

Mr. Sullivan, speaking to the Harvard Student Bar Association, expressed confidence that intellectuals would support the United States because of "disillusionment and disenchantment with Communism." When asked to be more specific about the intellectuals' role, Sullivan said they "should articulate and clarify our social vision based on freedom and our inalienable rights."

But Sullivan warned that Communists consider intellectuals "a primary target group" and seek to convert them "through front organizations concerned with such problems as civil rights, world peace, and civil liberties." "Gullibility is a real problem," he said, but if an individual is careful, "he should be able to recognize a front and come to grips with it."

After his speech Sullivan was questioned about possible abridgement of civil liberties by the Federal government in its search for subversives. "I am not here to discuss the House Un-American Activities Committee," he said. "But I am opposed to extremists on the right who advocate abridgement of the Constitution. It is contrary to our traditions and not very effective." Communists must, nevertheless, "be watched," he added.

Sullivan said that the FBI does not resent criticism and does not "persecute men who advocate the same point of view as Communists for good reasons." He emphasized FBI Director Hoover's tolerance and "faith in our system."