Tear gas canisters fired by police apparently set fire early this morning to an Anacostia row house where authorities believed an armed man had barricaded himself for hours after stabbing one man, shooting another and then firing shotgun blasts at arriving officers and rescue workers.

Police had tried vainly for some time to negotiate with the man before they began firing tear gas about 12:40 a.m. into the building at 2106 Minnesota Avenue SE. Four or five sharp reports were heard immediately but it was not clear whether they were caused by exploding ammunition, or by firing from inside, police said.

Following a period of several minutes, during which the fire appeared to blaze unchecked on the second floor of the row house and flames streamed from a window, firefighters began training streams of water on the structure.

While they did, the staccato reports which apparently emanated from within the house continued sporadically until about 1:40 a.m., six hours after the stand-off began. By that time the blaze appeared under control. There was no more sign of flame from the window.

Authorities indicated that neighboring houses had been evacuated some time earlier. There was no sign of anybody inside the burning house and as of 2:30 a.m. no indication of the gunman's fate. It could not be learned whether any of the adjacent houses had been damaged by the blaze.

Police said they arrived at the scene about 7:45 p.m. to find a man who had been stabbed in the chest lying critically wounded on the sidewalk. A second man, who had been shot and was also critically wounded was lying in the doorway of the Minnesota Avenue row house.

A third man who was in the stairwell of the house when they arrived was armed with what appeared to be a rifle or shotgun, officers said.

As firefighters who had reached the victim who lay in the doorway were returning with him to their truck, they heard gunshots. "Everybody took cover," said fire department Lt. Theodore Morris.

The man who was stabbed underwent surgery late last night at the Greater Southeast Community Hospital where officials identified him as Lawrence Coleman, 45, of 2110 Minnesota Ave. SE. He was in the recovery room early this morning, with his condition listed as critical, but stable.

The gunshot victim underwent surgery late last night at D.C. General Hospital where officials said he had apparently been shot several times. His identity was not immediately clear.

There was no definite indication early this morning of what provoked the shooting incident on the tree-lined street a few blocks east of the Anacostia River.

However, D.C. Police Chief Maurice T. Turner said authorities believed that the gunman may have been under the influence of drugs.

The stabbing victim was quoted by rescue workers as saying: "I was trying to stop him from killing somebody."

The incident filled the neighborhood with helmeted police who wore flak jackets and carried shotguns. A helicopter clattered overhead, and for a time a spotlight was trained on the row house as officers crouched behind trees and parked cars and warily made their way from one sheltered spot to another.

Neighbors peered cautiously from behind closed windows. Sharpshooters stationed themselves on a roof across the street from the row house, and at least one neighborhood resident reported that an officer with a shotgun was inside his house, posted at the window.

Using a megaphone police tried to make contact with the armed man inside the row house. However, there was no word of any response.

Shortly before 11 p.m., a man who police said had entered an adjacent house after the incident began, was led away in handcuffs. Moments later, police had Pepco workers cut power to the entire block.

Officials said they expected to "wait the man out."

Before the firing of the tear gas early this morning, the most dramatic incidents in the siege appeared to occur immediately after police and firefighters came to the street.

According to Lt. Morris, the stabbing victim was conscious and lying on the sidewalk when police and firefighters arrived. Rescuers began treating his wounds, bandaged him and waited for an ambulance.

Then, Morris said, they heard an unidentified police captain, shouting from the doorway of the house to a man inside, calling on him to throw out his gun. Then, the captain shouted to the firefighters, telling them that a second victim lay in the doorway.

Grasping the man by his legs, the captain began dragging him from the doorway onto a small porch.

The firefighters, using what cover they could find, made their way to the porch, placed the man on a stretcher, and were carrying him to their truck when they heard two gunshots behind them.

"I looked around to see who was there and we just ran down the sidewalk and got as low as we could behind the truck," Morris said. "It was very frightening."

An ambulance drew up, and the victim was placed inside. The firefighters, who included Ricky Green, Harold Whitfield, Walter Lewis and Larry Morris, remained behind the parked firetruck in which they came, for about 20 minutes until the police armored personnel carrier arrived.

After hours of what seemed a tension-filled standoff, members of a police special weapons and tactics team, clad in camouflage clothing, approached the building.

They prepared to fire tear gas, apparently to force the occupant out, or to pave the way for their entry. One canister detonated prematurely, and the attempt was temporarily halted.

Within a few minutes, the effort was resumed, and as many as four tear gas canisters were fired at the building.

The fire flared shortly afterward. Authorities cited the possibility that tear gas could ignite a blaze as one reason fire equipment remained in the area throughout the siege.