Arthur G. Murphy Sr., 48, chairman of the black causus of the Maryland General Assembly, died in Baltimore yesterday after suffering an apparent heart attack.

Mr. Murphy, who represented Baltimore in the Maryland House of Delegates, was brought to the emergency room of Provident Hospital shortly after 1 p.m. in a comatose state, a hospital spokesman said.

Attempts to resuscitate him were unsuccessful and he was pronounced dead at 1:58 p.m.

In 1977 Mr. Murphy led a filibuster against the death penalty. He was also a leader in the fight against the capital punishment measure passed in the 1978 General Assembly.

Maryland Acting Gov. Blair Lee III described his death as a "great loses not only for the black community but for all the people of Maryland."

After selection in January as chairman of the 19-member black caucus, Mr. Murphy said the group's first priority would be to push for a House override of a veto on a bill that would require higher welfare payments through fiscal 1982.

He was also known as a strong advocate of providing opportunities for minority-owned business.

Mr. Murphy served from 1962 to 1966 as an assistant U.S. attorney, and in 1969, Gov. Martin Mandel, who described Mr. Murphy's record as a prosecutor as "brilliant," appointed him as his top personal aide for law torney for Maryland.

Mr. Murphy served as the governor's civil rights adviser, and in particular acted as a liaison with both militant and moderate elements of Baltimore's black community in a time of high tension in 1969.

Mr. Murphy gave up his post as the governor's special assistant for community relations in 1973 to join the Maryland State Insurance Fund.

Survivors include a wife and three children.