A 21-year-old plumber's helper was shot to death yesterday morning as he searched for tools in his truck parked behind a church in a Capitol Hill alley.

Minutes before the shooting, a man had walked into the turn-of-the-century red brick building across the street at 921 Pennsylvania Ave. SE, the headquarters of the citys work training program for welfare recipients, and robbed a D.C. government security guard of his service revolver at knifepoint.

Gilbert P. Reynolds, 27, of 640 Croissant Pl. SE, was arrested and charged with second degree murder in the shooting death of Victor L. Larranaga, of 1856 Mintwood Pl. NW. He had turned himself into police shortly after the incidents, police said.

Police said they had no motive in the shooting of Larranaga.

Larranaga had been working with Robert H. Payne, 22, of Springfield, Va. in the basement of the Tried Stone Church of Christ, 417 Ninth St. SE.

"I sent Vic out to get some tools," Payne said, "then all I heard was the gunshot and I heard his body falling down the stairs. I ran out and saw him lying in the stairwell with a hole in the back of his head."

Twenty minutes later and eight blocks away, Pearl Rush, a receptionist in the lobby of The Washington Star newspaper, 225 Virginia Ave. SE, said an unarmed man walked in and told her, "'I just shot a man. Call the police.' I told him just a minute and to have a seat because I had somebody else here I was trying to help. I really didn't believe him," she said.

A security guard in the lobby, called by Rush telephoned police who arrested Reynolds minutes later.