George Plimpton, a literary lion who entered the coliseum of professional sports as an amateur, died in his sleep Sept. 26 in his Manhattan apartment.

Mr. Plimpton -- who reunited last Sunday with the players who helped shape his book "Paper Lion," about a 36-year-old writer's football tryout with the 1963 Detroit Lions -- had not been ill, but the 76-year-old had heart problems, his lawyer said.

"He thought he had a 26-year-old heart and acted like it," attorney James Goodale said.

Born into a blue-blooded American family in New York City (his father was a wealthy corporate lawyer and a diplomat at the United Nations), Mr. Plimpton was called "the ultimate Good Fellow" by David Remnick, now editor of The New Yorker, in a 1984 Washington Post profile.

Mr. Plimpton was expelled from Phillips Exeter Academy in New Hampshire but graduated from Harvard and Cambridge universities. After a stint as an Army tank driver in Italy during World War II, Mr. Plimpton helped start the literary quarterly the Paris Review and served as its only editor. He persuaded Sadruddin Aga Kahn, the son of Prince Aga Kahn, to become publisher of the financially shaky enterprise while the two were running in front of the bulls in Pamplona, Spain.

"It was a good time to ask him for anything because his mind was not on whatever I was asking him to do," Mr. Plimpton told National Public Radio last month. "The bulls were right behind him, and he said: 'Yes! Yes, I will! I'll do that!' "

The Paris Review -- which published such emerging authors as Philip Roth and Jack Kerouac -- has such a small circulation that Mr. Plimpton saw only one person ever buy the quarterly. But that customer was Ernest Hemingway.

Mr. Plimpton wrote with grace and wit and was popularly known as a writer who acted on Everyman's Walter Mitty daydreams.

Mr. Plimpton had his nose bloodied by light-heavyweight boxer Archie Moore, cut his hand when he played goalie with the Boston Bruins, clung to a trapeze with the Flying Apollos and pitched to baseball great Willie Mays. But the encounter that most frightened the "participatory journalist" was playing the triangle in the New York Philharmonic under conductor Leonard Bernstein.

"I was terrified of him," Mr. Plimpton told The Post in 1984. "You couldn't make a mistake. In a football game or baseball game, mistakes are part of what happens. Bernstein was a terror."

When he missed his cue on Mahler's Fourth Symphony during the orchestra's Canadian tour, Bernstein kicked him out. Mr. Plimpton talked his way back in time for the Winnipeg concert, agreeing to softly strike the gong at a moment in Tchaikovsky's Symphony No. 2 "Little Russian," a writer for the Winnipeg Free Press recalled.

"He resolved to watch the conductor like a hawk to make sure he'd be right there when cued," the writer said. "The gong, though, is the percussion equivalent of flash paper.

"George came in on target. But when the gong roared over the orchestra like an arm's-length 747, I watched as the horrified Bernstein dropped his hands and 100-plus players turned their heads. . . . To this day, musicians talk about the Winnipeg sound."

It seemed as though Mr. Plimpton knew everyone. He played -- and lost -- a horseshoe match with not-yet-President George W. Bush, and was the subject, by name, of at least two New Yorker cartoons. He escorted Queen Elizabeth II while she was a princess, Ava Gardner while she was a movie star, both Bouvier sisters (later known as Jacqueline Kennedy Onassis and Lee Radziwill), actresses Jane Fonda and Candice Bergen and poet Marianne Moore. He appeared in more than a dozen movies ("Reds," "Rio Lobo," "Good Will Hunting") and on television's "The Simpsons." A fancier of fireworks, Mr. Plimpton's exhibition in Central Park became an opening shot in the Woody Allen movie "Manhattan."

"Friends were almost always happy to see him because you knew he was bound to improve your mood," author Norman Mailer told the Associated Press yesterday. "What fine manners he had! Few could give a toast or tell a story with equal humor."

In 1968, Mr. Plimpton grabbed Sirhan B. Sirhan after the assassin shot Robert F. Kennedy in Los Angeles, and he was one of the men who pried the gun from Sirhan's hand and held him down. "I had my hands around his neck," he told the Associated Press last year, his voice fogging up. "Bad stuff."

In August, he signed a $750,000 deal with Little, Brown and Co. to write his memoirs. But first, he said, he had to finish a book about bird-watching.

He was named a "central figure in American letters" when inducted last year into the American Academy of Arts and Letters, and the French subsequently made him a Chevalier, the Legion of Honor's highest rank.

But his real legacy, attorney Goodale said, will be his unpaid work on the tiny Paris Review, the magazine that introduced promising writers and established the tradition of interviews with renowned writers about the craft. The night before he died, he put the 50th anniversary edition to bed.

"George Plimpton was one of a kind," Sen. Edward M. Kennedy (D-Mass) said in a statement. "He was a lifelong friend of our family since the day he met Bobby at Harvard. . . . He reminded me of the line from Shakespeare, 'Age could not wither him, nor custom stale his infinite variety.' We'll miss him very much."

Mr. Plimpton's 20-year marriage to Freddy Medora Espy ended in divorce in 1988. In 1991, he married Sara Whitehead Dudley. He had four children, two from each marriage.

George Plimpton, in 1997, was renowned as an author, gentleman editor and "participatory journalist."