Police arrested 50 people occupying the George Sherman Union at Boston University yesterday as the school witnessed its third consecutive day of student antiwar protest.

Last might a group of about 800 students held a mass meeting in B.U.S Marsh Chapel and voted to strike until the university complies with a list of several demands, including the lifting of a broad-based injunction against unlawful protest rallies on campus.

A crowd varying in size between 300 and 700 played tag with police for over an hour yesterday afternoon on Commonwealth Ave. as demonstrators attempted first to occupy the registrar's office and university computer center at 881 Commonwealth Ave., and then to retake the Sherman Union located further up the street.

Earlier in the day, before arresting the occupants of the Union, police used mace to repel a group of students attempting to join those still inside the building. One policeman was reportedly injured by a brick during the incident.

Those arrested in yesterday's action were booked on charges ranging from criminal trespass and breaking and entering with intent to commit a misdemeanor to assault and battery on a police officer. Late Friday night administration officials had said that protesters remaining in the Union past midnight would merely be cited for contempt of court.

The 50 people arrested yesterday will be arraigned in Roxbury District Court tomorrow.

Downstairs

At about 7 a.m. yesterday, approximately 40 demonstrators occupying the office of Staton R. Curtis, dean of student affairs at B.U., voted to move downstairs to the Zuskind lounge where supporters of the action had gathered the night before.

Administrators and faculty members later pleaded with them to vacate the building in order to avoid arrest. One occupier of the Union, who asked to remain unidentified, said that at one point officials told the protesters inside that police were anxious to avenge the policeman who was reportedly injured by demonstrators outside the building.

At about 2 p.m., those still in the building, including several faculty members, voted to be escorted out in groups of three flanked by one policeman and one faculty member. As the protesters were being led out the back of the building with their hands behind their heads demonstrators chanting in front of the building raced around the side trying in vain to prevent the arrests.

The crowd then regrouped in front of the Union to decide on further action. At 3.25 p.m. about 300 demonstrators ran down Commonwealth Ave. to the registrar's office and computer center, which 100 of their number held briefly until riot-equipped police arrived on the scene.

The protesters--whose ranks were swelled by picketers outside the building--quickly left the registrar's office and rushed back to the Union where they found police still holding the building.

At about 5 p.m., the crowd voted to disband and reconvene at the mass meeting later in the evening.