In the basement of Blair House, the president's elegant guest quarters, is the rather plain day room of the Secret Service Uniformed Division.

Yesterday in a ceremony it became something more: the Leslie W. Coffelt Memorial Room, honoring the White House police private who on Nov. 1, 1950, died saving the life of Harry S. Truman. By the door is a plaque. Inside are a photograph of Coffelt, a scrapbook telling his story and a frame holding his three medals and a letter from his stepdaughter, Cora Jane Coffelt Miller, presenting the medals for his heroism to his successors.

Forty years ago, on an Indian summer day much like yesterday, President Truman was living in Blair House while the White House was being remodeled and repaired. The city bus regularly stopped in front of the residence at Pennsylvania Avenue across from the Old Executive Building, a heavy transfer spot. White House police officer Floyd Boring, now retired, was on duty that day, standing guard at the front door.

"The president was upstairs, having a nap before he was due to go to Arlington to lay a wreath," Boring said yesterday morning while waiting for the dedication to begin. "We were outside on the steps when two gentlemen came up and one pulled out a gun and aimed it at me. I heard it snap, and I pulled out my gun and shot back. Then everybody was shooting. I saw Officer Coffelt fall, but first he shot and killed one of the men. It was all over in 20 seconds. It was thrilling. I realized later that the man aiming at me had forgotten to cock his Luger pistol. Mr. Truman was never in any real danger, because he was to leave by the back door -- they wouldn't have a chance at him."

Two other guards, Donald T. Birdzell and Joseph H. Downs, were shot but recovered. The 40-year-old Coffelt died that night at Emergency Hospital (now demolished) a few blocks away.

White House curator Rex Scouten, then a Secret Service officer, recalled that he was just going into the West Wing of the White House to do the daily reports "when the phone rang and said shooting was going on across the street. I came right over." An hour later, President Truman went on to the ceremony at Arlington.

Lawrence A. Hartnett, at the time a D.C. detective, was in a police cruiser at Ninth and Pennsylvania, coming to escort Truman. By the time he reached Blair House "there was a lot of confusion, but organized confusion," he said after the ceremony yesterday.

The would-be assassins, Oscar Collazo and Griselio Torresola, were Puerto Rican nationalists. Collazo, the survivor, stood trial for first-degree murder and was given the death penalty. Later Truman commuted the sentence to life imprisonment. In 1979 Collazo was released and went back to Puerto Rico.

Coffelt's sister, Mildred Good, heard the news of her brother's death on the radio in Strasburg, Va., their hometown. "I thought of the day years before when he saved up his money and bought a shotgun," she said yesterday. He loved that gun, kept it polished and cleaned. I warned him guns would be his death. But you know, he loved his job, he wouldn't have chosen any other way to go. I am sure he had no regrets."

Coffelt's stepdaughter said she was 19, working at the Veterans Administration, when they called her. "I always rode to work and then home again with him. But not that day," she said.

"The story of those violent minutes will never diminish in importance to any of us," said Secret Service Director John R. Simpson during yesterday's ceremony, attended by about 150 people in Blair House's garden room. "He wasn't an extraordinary man, but like Euripides said, 'This is courage in a man, to bear unflinchingly what Heaven grants.' I pray the Secret Service will always have his courage."

State Department Protocol Chief Joseph Verner Reed presided over the program, sponsored by Louis Blair of the Harry S. Truman Scholarship Foundation and suggested by Donald Blake, the coordinator of Blair House security. Dorothy Bush LeBlondrepresented her parents, President and Mrs. Bush.

Outside Blair House, Uniformed Division Capt. Ronald Normandin stood with Sgt. John Howard. "Constant vigilance, that's what it takes," Normandin said. "And when you see a nervous twitch that doesn't fit, you know to watch out. Coffelt did everything right. He knew exactly what he was doing and had to do. He stood his guard and protected the president."