Two U.S. senators attempted unsuccessfully yesterday to revive a 57-year-old university professor who collaposed after apparently suffering a heart attack after he testified at a hearing on Capitol Hill.

Martin Diamond, 57, who left the Northern Illinois University faculty this week to become a professor of governmenttt at Georgetown University, was pronounced dead at the Capitol Hill Hospital where he was taken by a D.C. Fire Department ambulance.

Diamond had testified at a hearing of the Senate Judiciary Subcommittee on the Constitution against a proposed constitutional amendment providing for direct election of the President, instead of indirectly through the Electoral College. Diamond was invited to testify by Sen. William L. Scott (R-Va.).

after testifying, Diamond returned to a seat in the audience, where he collapsed. About 30 people were in the hearing room in the Russell Senate Office Building when the incidentt occurred.

Sen. Birch Dayh (D-Ind.), the subcommittee chairman, rushed to Diamond's side and attempted mouth-to-mouth resuscitatatation for about 10 minutes. Sen. Orrin G. Hatch (R-Utah), the only other lawmaker present, applied rhythmic pressure to Diamond's chest.

Bayh and Nels Acikerson, the subcommittee's chief counsel, both contended there was an excessive delay in the arrival of medical personnel.

"It really shakes you up to think you're trying to breathe for someone and then find out later he's dead," Bayh said.

Ackerson said the first of several telephone calls was made to the Office of the Attending Physician in the Capitol at 10:50 a.m., and the first technicians arrived about 20 minutes later, at about the same time as an ambulance crew. Diamond was admitted to the hospital about eight blocks away at 11:20.

"That kind of delay should not have happened," Ackerson said.

Robert Moran, administrator of the Capitol physician's office, blamed the delay on confusion over where the collapse occurred. He said the first call summoned assistance to roommo S-235, which would be in the Senate wing of the Capitol building itself, while the incident actually occurred in room 235 of the Russell Building about a block away. Gooing to the wrong location cost valuable time, Moran said.