A 10-hour standoff during which a nuclear weapons protester threatened to blow up the Washington Monument with a truckload of dynamite ended last night when the man was killed as he tried to drive the truck away from the monument through a volley of police gunfire. Police discovered later that the truck contained no explosives.

The man, identified by police early this morning as Norman Mayer, 66, a hotel maintenance man from Miami Beach, was pronounced dead in the truck shortly after it was brought to a stop by a hail of bullets and toppled onto its side.

After an autopsy completed about 2:30 a.m. today, police officials announced that Mayer was killed by a single bullet wound to the head.

The day-long siege, which forced closure of buildings and roads in the monument area and brought evening rush-hour traffic to a near standstill, was declared over about midnight after police abandoned a search for a second man who was thought for a time to have been involved in the threat. Police said all roads affected by the siege would be open for morning rush hour today.

The protester, clad in a dark blue jumpsuit and visored helmet, had paced around the foot of the monument thoughout the day, threatening to use a remote-control device to detonate 1,000 pounds of dynamite he claimed to have in the truck that he parked at the monument entrance shortly before 9:30 a.m.

Eight persons who had been inside the monument at the time the truck arrived were trapped at its top for five hours. At midafternoon they were released, and later, after negotiations conducted through Associated Press reporter Steve Komarow, the man issued rambling demands for a ban on nuclear weapons, "or face doomsday."

The standoff continued until about 7:30 p.m. when, in the evening darkness, the truck began to move away from the monument. An undetermined number of police officers opened fire and the truck swerved and tipped over about 50 yards northeast of the monument.

About 90 minutes later, D.C. Police Inspector James P. Shugart announced that the driver, later identified as Mayer, had been pronounced dead at the scene.

Police officials said the officers firing at the moving truck had been aiming at its tires and engine in an effort to prevent it from entering more populated areas. The number of shots fired at the truck and the exact nature of the weapons used remained unclear early this morning. Investigators said the fatal bullet had not yet been recovered and that police evidence technicians were continuing a search of the truck and the monument grounds for it.

After the shooting, police fired tear gas into the monument, then searched the structure for about three hours in the belief that a second man might have been involved in the incident. One police officer had reported seeing what he thought was a man in the monument entrance as the truck was pulling away, and later police placed a call to a phone at the top of the monument, which they said was answered by someone who said nothing and then hung up. Police officials said later that they thought the phone had malfunctioned.

Police approached the truck cautiously after the shooting in the belief that there was still the possibility of an explosion and found that Mayer was handcuffed to the steering wheel and that he was holding an electronic device that he had claimed earlier was a transmitter that could detonate the explosives. Police later described the device as similar to a remote-control unit for model airplanes, and said that it was capable of setting off an explosion.

Although dogs specially trained to detect explosives had shown a "positive reaction" when they were sent into the truck, police demolition experts later searched its contents and found none.

Earlier, police had announced that they had received from the man a list of demands on a printed piece of paper. Among them was a call for a national dialogue on nuclear weapons and an instruction that the media spend most of its time on this issue. "There are 1,000 pounds of TNT in this truck that can be detonated four different ways on automatic," the note said.

Law enforcement officials, fearful that a blast would send shrapnel flying and break glass in nearby office buildings, closed seven museums and eight major office buildings around the monument, including the Smithsonian and the Departments of Agriculture and Commerce. As a result, at least 20,000 government employes were sent home at mid-day.

In addition, officials closed all the streets around the monument, including those in a square bounded by Seventh and 23rd Streets NW and Constitution and Independence Avenues, creating an enormous rush hour traffic jam that left people unable to get into or out of the city for hours. Some government workers who got off at noon were still struggling to get out of the city at 5 p.m.

Mayer was described by friends and relatives yesterday as a drifter whose obsession with his one-man crusade against the spread of nuclear weapons took him from college campuses in Florida to the White House sidewalk.

He had been living on and off for the last eight months in a $30-a-night room in a downtown motel -- where he was known as "Pops," a mild-mannered man who always paid with $100 bills -- and spent much of his time parading in front of the White House with a wooden protest sign.

Mayer refused to talk with police who had walked to the base of the monument and opened their coats to show they were unarmed. He became extremely agitated at the sight of the policemen and shouted, " 'Get the hell out of here'," a police spokesman said. "He just went crazy," the spokesman said.

Instead, he insisted on negotiating with a member of the press who was " 'single and without dependents'," the spokesman said, and Komarow was chosen.

By 7:30 p.m., Komarow had talked with Mayer five times. He reported that Mayer referred to politicians as "genocidalists," and that his demands were largely unfocused beyond his insistence on a discussion of the abolition of nuclear weapons.

" 'They have been pretending that we are not threatened every day of our lives with annihilation,' " Komarow quoted the man as saying. "And whether by collusion or otherwise, they refuse to give the real information about the precarious and uncontrollable situation the world finds itself in. It's up to the press."

Komarow said the man told him he chose the monument as the site of his protest because "it's one of the sacred icons and it's accessible." On several occasions, the man warned against police rushing him, Komarow said. "If anybody gets cute, tries to play games, they'll have a pile of rock," Komarow quoted him as saying.

At the end of the fifth visit, Komarow said, the man told him, "Well, you've got the gist of it. See you tomorrow."

At the White House yesterday, President Reagan's lunch with his Private Sector Initiatives Task Force was moved from the State Dining Room to the Grand Foyer, according to the Associated Press.

Officials also directed First Lady Nancy Regan and others in the White House to avoid the south side of the building for fear that a concussion from a blast could shatter glass.

Specialists in explosives said yesterday that if the truck had contained 1,000 pounds of dynamite and was detonated near the base of the monument, the blast would not be expected to do more than scar the base of the memorial, which is 15 feet thick at that point with walls of granite faced with marble.

The truck, with a sign on it that read "No. 1 Priority, Ban Nuclear Weapons," pulled up to the base of the monument about 9:20 a.m. and a man wearing a blue snowmobile jumpsuit, a black motorcycle helmet with full visor and a backpack with a two-foot antenna attached to it, jumped out and told a tourist nearby to, "Get the hell out of here."

Henry Lichtenstein, who operates a tour bus, was near the monument when the truck pulled up and talked to the man in the helmet. "He said, 'I've got a lot of dynamite in the truck,' " Lichtenstein told a Washington Post reporter. "He wouldn't let anybody get close. He said if they got near he'd blow them up."

Mike Rosenfeld, a tourist from Myrtle Beach, S.C., was leaving the monument after walking down the stairs because the elevator was not working. Rosenfeld recounted:

"We got down there and the guard said, 'Get out, run.' I said 'Why?' The guard seemed agitated and said, 'Just get out.' "

Rosenfeld said he noticed a truck and walked up to the man near it. "I went up and said, 'What are you doing?' He didn't answer. He just motioned violently for me to get away. I asked again and he wouldn't talk. Finally I left."

The man then approached one of the rangers who operates the obelisk and told him to clear the monument before he blew it up, a police spokesman said. The man then gave the park ranger a hand-printed message that read:

"If any person starts up this hill, the government agencies will be responsible for the consequences.

"No. 1 priority: Will only negotiate with a representative of the media.

"Let the Washington, D.C. (U.S.A) media form an ad hoc committee and vote a single person without dependents to intermediate." Contributing to these reports were Washington Post staff writers Joseph E. Bouchard, Chip Brown, Edward Cody, Margaret Engel, Paul Hodge, Mary McGrory, Alfred E. Lewis, Walter Pincus, Sandra Sugawara, Mary Thornton and Juan Williams, and special correspondent Katherine Macdonald.