David F. Powers, whose loyalty, sense of humor and contacts throughout Boston's Irish community made him a close friend and aide to John F. Kennedy and a fixture at the Kennedy White House, died today at the Symmes Medical Center in Arlington, Mass. He was 85.

He died of cardiac arrest, said Tom McNaught, a spokesman for the John F. Kennedy Library in Boston, where Mr. Powers was the museum curator from 1965 until he retired in 1994.

Senator Edward M. Kennedy, Democrat of Massachusetts, said in a written statement, ''Jack loved Dave Powers like a brother, and so did all of us in the Kennedy family.''

The son of immigrants from County Cork, Ireland, David Francis Powers was born on April 25, 1912, in the Charlestown section of Boston, a waterfront district of three-decker tenements. His father died when he was 2, and at age 10 David got a job as a newsboy, a position that he later said helped him get to know nearly everyone in the area. After graduating from high school, he held a variety of jobs and attended college at night before joining the Army Air Force in 1942. He served for three years in Asia before being discharged at the end of World War II as a master sergeant.

While baby-sitting for his widowed sister's children back in Charlestown one night in 1946, Mr. Powers answered a knock on the door.

''In the semidarkness I could see this tall, thin, handsome fellow,'' Mr. Powers later recounted, ''and he reached out his hand and said, 'My name is Jack Kennedy. I am a candidate for Congress. Will you help me?' ''

Mr. Powers and the young politician hit it off immediately, and Mr. Powers's intimate knowledge of the neighborhood and its residents -- in addition to having been its newsboy, he ushered at five Masses every Sunday at St. Catherine's Church -- was a gold mine for Kennedy.

When Kennedy went to Washington, Mr. Powers remained in Boston, where he worked for the city housing authority and the state housing board. But Mr. Powers worked on each of Kennedy's subsequent campaigns, for the House, the Senate and then the Presidency.

After winning the 1960 election, Kennedy named Mr. Powers a special assistant in the White House. His ostensible job was to greet visitors and escort them to the President, a role that he filled with sometimes startling unpretentiousness and lack of formality. He introduced Prime Minister Harold Macmillan of Britain as ''the greatest name in England,'' and to the Shah of Iran he said, ''I want you to know you're my kind of Shah.''

But his real role was First Friend, someone with no agenda of his own who could share a silence, reel off baseball and football statistics or make Kennedy laugh with one of his endless supply of tales and jokes.

In his 1993 biography, ''President Kennedy: Portrait of Power,'' Richard Reeves described a moment in the Cuban missile crisis when Mr. Powers was eating roast chicken with the President upstairs in the White House as Attorney General Robert F. Kennedy came in with a downbeat assessment of the situation. Mr. Powers continued eating.

''God, Dave, the way you're eating up all that chicken and drinking up all my wine, anybody would think it was your last meal,'' the President said in Mr. Reeves's account.

''The way Bobby's been talking,'' Mr. Powers replied, ''I thought it was my last meal.''

For all his intimacy with the President, Mr. Powers never exaggerated his influence or ran from his occasional role as glorified butler. Asked once about the most difficult moment he had faced in politics, he replied with a story about forgetting to bring black shoes to go with Kennedy's blue suit in the Democratic National Convention in 1952, forcing Kennedy to make a televised speech in brown shoes.

''And after it was over,'' Mr. Powers said later, ''to help him relax, I said, 'Mr. Senator, that was a brown shoe crowd if I ever saw one.' ''

Mr. Powers was in the motorcade in Dallas when Kennedy was killed, and after the assassination, Mr. Powers remained close to the Kennedy family, visiting often with the slain President's children, Caroline and John F. Kennedy Jr.

He went on to assemble and catalogue thousands of pieces of Kennedy memorabilia and to raise money for the library, which opened in 1979. In 1970, Mr. Powers, Kenneth P. O'Donnell and Joe McCarthy wrote ''Johnny, We Hardly Knew Ye,'' a nostalgic biography of Kennedy.

Mr. Powers is survived by his wife, Jo, of Arlington, Mass.; a son, David, of Andover, Mass.; two daughters, Mary Jo, of Falmouth, Mass., and Diane, of Maine, and three grandchildren.

David F Powers