HENDERSON, Nev. (AP) _ A former security guard who begged police to shoot him as he held a pistol to the head of his infant son was fatally wounded by a police sniper, ending a five-hour siege.

''Do your job 3/8'' shouted the man police identified later Wednesday as 35- year-old John Thomas Walker of Las Vegas. ''Shoot me, man, shoot me, man.''

Shortly after 3:30 p.m. Wednesday, as Walker held the baby in a residential street of this Las Vegas suburb, the police marksman fired, hitting Walker in the head.

He was pronounced dead 20 minutes later at St. Rose de Lima Hospital.

The gunman's 14-year-old son, who also brandished a gun during the standoff, dropped his weapon and put his hands in the air, police said.

The youth, whose name was not disclosed because of his age, was taken into custody and held at Clark County Juvenile Center.

Police said Walker fell on the infant after he was shot, but the boy was unhurt and released to his mother after a hospital checkup.

Walker apparently was despondent over his wife leaving him and the children and his inability to find a job, police and neighbors said.

''He said his wife left him with the baby and 14-year-old son,'' said Geraldine Johnson, manager of an apartment complex where Walker applied for a job Tuesday. ''He seemed down ... I felt bad for him.''

The incident began about mid-morning when Walker allegedly called a television station and told a newsman ''There's going to be front page news today. There's going to be a murder.''

Police said Walker went to a house in this Las Vegas suburb, where three unidentified girls fled and the siege began when he fired one shot at officers.

Walker, in telephone negotiations, repeatedly threatened to come out with the baby and start shooting, police said.

Police thought at first that the man was holding the two children hostage, but it later became apparent the 14-year-old was helping his father, said Henderson Police Sgt. Ed Eckels.

Several times during the standoff Walker walked outside the house with the infant in his arms and the gun held high in the air. Once, he fired five shots into the air before going back inside the house, police said.

Police cordoned off the area and installed sharpshooters in neighboring houses and on the roof of an adjacent shopping center while negotiators tried to talk the man into surrendering. Some neighbors were evacuated from their homes and children from a nearby school were rerouted on trips home.

Police said late in the siege Walker said he was going to come out with a semi-automatic rifle and start shooting. He also demanded to talk to his wife, a request police denied.

''We felt it would do nothing but aggravate the situation,'' said Henderson police Lt. Ron Delia.

After the man returned to the house, tactical commanders ordered a Las Vegas police sharpshooter to shoot if Walker came out and pointed the weapon at officers.

A few minutes later, that order was amended to shooting Walker if he left the property whether or not he held the baby, police said.

Walker emerged from the home a final time with his gun drawn and the baby in his arms. He walked down a driveway, into the street, then turned and took a few steps up the street before the single shot felled him, police said.