A 36-year-old Gaithersburg man, depressed over marital problems, shot himself to death yesterday as Montgomery County police waited outside his home, believing he had barricaded himself inside and was still alive and armed.

Members of the Special Weapons and Tactics (SWAT) squad who finally entered the house found the body of Richard J. Delarue in an upstairs bedroom. Police had been outside the house for 1 1/2 hours by that time and had been trying unsuccessfully to contact Delarue with a bullhorn for about an hour and 15 minutes.

Police were summoned to Delarue's home at 9452 Horizon Run Dr. in Montgomery Village about 2:30 p.m. by the man's estranged wife who said her husband was threatening suicide and had fired two shots from inside the house.

When police arrived, Delarue fired at least three more shots, two out the front window and one out the back, according to police spokesman Phillip B. Caswell, who said the shots were not directed at the police. Caswell said police fired no shots.

At the direction of Police Chief Robert J. diGrazia, who was one of the first officers at the scene, the SWAT team, which specializes in handling hostage situations was called in.

Meanwhile, two fire trucks and two ambulances and dozens of police officers arrived at the scene. Residents of nearby houses were evacuated as a throng of reporters and neighbors looked on.

When police failed to receive any communication from the main or perceive any movement in the house, they eentered and found Delarue dead of an apparent gunshot wound to the head. Police said 30-caliber rifle was beside him. Delarus had barricaded himself in the room by placing a dresser against the bedroom door, police said.

Police said Delarue had become increasingly disressed after separating from his wife in January. He was living with his five children, ranging in age from 7 to 14. Three of the children were at school a block away when the incident occurred.