The administration of Boston University (B.U.) has begun procedures to fire or suspend five tenured B.U. professors because they refused to cross picket lines of striking clerical workers earlier this fall.

The five professors cancelled their regular classes for up to several days because of the strike, faculty sources said yesterday. The professors either held their classes at the regular time off-campus or made up classes later, the sources said.

Two of the professors--Murray Levin and Howard Zinn--are nationally-known political scientists. All five have been active to some extent on faculty issues.

Besides Levin and Zinn, the faculty members involved are Andrew S. Dibner, Fritz Ringer, and Caryl Rivers. Ringer was president of the faculty union last year and Zinn chaired the committee that organized a strike by B.U.'s faculty, secretaries and librarians last spring.

"This is outrageous. It's like trying to kill a flea with a machine gun," Dibner said yesterday. He said that one day during the clerical workers' strike he held classes off-campus at the regular time.

"I didn't want to cross the picket lines and I didn't want my students to have to cross the picket lines," Dibner said, adding that his action was a matter of conscience.

"They seem to be shooting at those of us who stand up for our rights and who protest the autocratic procedures of the administration," he added.

The contract between B.U. and its faculty allows the administration to fire or suspend tenured professors "upon gross neglect of duties, or other just cause."

Associate Provost John C. Westling notified the professors they may be fired or suspended in letters dated October 31. Westling yesterday declined to comment except to confirm that he had sent the letters. Steven Wagner, director of public relations, also refused to comment.

Leonard Blocksberg, professor of social work, received a similar letter, but sources said the action against him was unrelated to the letters sent to the other five professors. Blocksberg yesterday declined to say why the administration was taking action against him.

The faculty contract provides that the next step in the proceedings against the professors will be review by an ad-hoc committee of faculty members.

James A. Garland, chairman of the B.U. chapter of the American Association of University Pofessors, said yesterday the faculty union will provide moral and legal support to all six professors. Emphasizing that the tenure system was designed to prevent universities from penalizing outspoken professors, Garland said firing the BU. professors "would be a terrible violation of academic freedom."

Relations between the university and the faculty have been strained since 1975, when the faculty unionized over the heated objection of B.U. President John R. Silber. Faculty activists charge that Silber has tried to destroy the union, and 25 professors recently formed a committee seeking to oust Silber.

Several professors said yesterday they were sure Silber made the decision to initiate disciplinary proceedings. A B.U. official would say only that Silber was among those who made the decision.