NEW YORK, Feb. 28 -- Arthur M. Schlesinger Jr., the Pulitzer Prize-winning historian and Kennedy insider who helped define mainstream liberalism during the Cold War and remained an eminent public thinker into the 21st century, has died, his son said. He was 89.

Schlesinger suffered a heart attack while dining out with family members Wednesday night in Manhattan, Stephen Schlesinger said. He was taken to New York Downtown Hospital, where he died.

Among the most famous historians of his time, Schlesinger was widely respected as learned and readable, with a panoramic vision of American culture and politics. He received a National Book Award for "Robert Kennedy and His Times" and both a National Book Award and a Pulitzer for "A Thousand Days," his memoir/chronicle of President John F. Kennedy's administration. He also won a Pulitzer, in 1946, for "The Age of Jackson," his landmark chronicle of Andrew Jackson's administration.

With his bow ties and horn-rimmed glasses, Schlesinger seemed the very image of a reserved, tweedy scholar. But he was an assured member of the so-called Eastern elite, friendly with everyone from Mary McCarthy to Katharine Graham and enough of a sport to swim fully clothed in the pool of then-Attorney General Robert F. Kennedy.

He was a longtime confidant of the Kennedys, a fellow Harvard man who served in the Kennedy administration and was often criticized for idealizing the family, especially for not mentioning the president's extramarital affairs.

"At no point in my experience did his preoccupation with women -- apart from Caroline crawling around the Oval Office -- interfere with his conduct of the public business," Schlesinger later wrote.