Comdeian and political activist Dick Gregory, his wife, Lillian, and a Massachusetts state senator were arrested at the South African Embassy yesterday afternoon for demonstrating within 500 feet of the embassy, according to D.C. police.

The three were arrested without incident at 12.40 p.m. when they were 236 feet from the embassy and charged with violating a law that states that protesters must stay at least 500 feet from an embassy, police said. Gregory and about 25 other persons, were peacefully protesting political conditions in South Africa, police said.

The maximum penalty for the offense is $100 fine and 60 days in jail, police said.

The Gregorys and state Sen. Bill Owens, a Boston Democrat, were told they could post bond or be released on a citation after their arrest, police said, but the Gregorys declined and remained in the second district police headquarters lockup. They were scheduled to be arraigned today.

The protesters, two carrying placards protesting the death of black leader Steve Biko of South Africa, had demostrated in front of the White House earlier yesterday, according to police. Police were informed that the marchers would next demostrate in front of the embassy. Police were at the embassy when the marchers arrived, police said.

The one-time presidential candidate and demostrator for civil rights and antiwar causes was arrested at the embassy Oct. 18, 1976, when he refused to leave until the government of that country guaranteed an end to violence resulting from racial disputes.