A University security guard has been suspended for five days because he attempted to break into a state police cruiser during Commencement ceremonies earlier this month, police sources said.

The guard was apprehended by Harvard police officer Patrick Griffin during the attempted break-in, sources said. Griffin was out of the office and could not be reached for comment yesterday.

Manager of Operations for Security Robert J. Dowling, the guard's boss, and Lt. Lawrence J. Murphy, the officer-in-charge, both refused to comment on the incident yesterday.

The sources, security and police officers who spoke on condition of anonymity, said they thought the guard should have been fired for the action. Police decided not to charge the guard with any crime, the sources said.

The guard in question did not return repeated phone calls to his home yesterday. State police spokes-people said yesterday that they had no knowledge of the incident.

Disciplinary problems appear to have become commonplace in the guard unit during the past year. In January, for example, two security guards fought with each other in the security office of 29 Garden St. One guard was terminated after the altercation because he allegedly lied about the incident in his report to Harvard police.

The fired guard, who has appealed his termination, said his account was accurate and said his firing was retaliation for his previous public charges that he was harassed by his superiors in the security department. An investigation of the fight by Lt. John F. Rooney, the head of the Harvard police's criminal investigations unit, did not reach a conclusion as to whom was at fault in the altercation.

In addition, security supervisor Donald P. Behenna allegedly was involved in altercations with a security guard he supervises and a Harvard police officer during the past year.

General Counsel Margaret H. Marshall is currently investigating charges made by several security guards that their bosses are discriminatory. The guard who allegedly broke into the police cruiser is not one of those charging discrimination.

Rooney did not return a phone call yesterday.