And it set up a First Amendment confrontation between the Nixon administration and The New York Times, whose publication of the papers was denounced by the government as an act of espionage that jeopardized national security. The U.S. Supreme Court upheld the freedom of the press.

Mr. Ellsberg was charged with espionage, conspiracy and other crimes and tried in federal court in Los Angeles. But on the eve of jury deliberations, the judge threw out the case, citing government misconduct, including illegal wiretapping, a break-in at the office of Mr. Ellsberg’s former psychiatrist and an offer by President Nixon to appoint the judge himself as director of the Federal Bureau of Investigation.

“The demystification and de-sanctification of the president has begun,” Mr. Ellsberg said after being released. “It’s like the defrocking of the Wizard of Oz.”

The story of Daniel Ellsberg in many ways mirrored the American experience in Vietnam, which began in the 1950s as a struggle to contain communism in Indochina and ended in 1973 with humiliating defeat in a corrosive war that killed more than 58,000 Americans and millions of Vietnamese, Cambodians and Laotians.

He was a brilliant young man from Michigan who had known tragedy at 15, when his mother and sister were killed in a car crash after his father fell asleep at the wheel, and who had rallied to march through prep school, Harvard and the University of Cambridge in England with high honors and lofty, disciplined ambitions.

He joined the Marines in 1954, swept through officer candidate school and extended his enlistment to ship out with his battalion to the Middle East for the Suez crisis in 1956. He saw no action, but mustered out as a first lieutenant with firm ideas about military solutions to international problems.

He earned a doctorate at Harvard, joined the RAND Corporation and began studying game theory as applied to crisis situations and nuclear warfare. In the 1960s, he conferred on Washington’s responses to the Cuban missile crisis and North Vietnamese attacks on American ships in the Gulf of Tonkin.

By 1964, Mr. Ellsberg was an adviser to Defense Secretary Robert S. McNamara. As American involvement in Vietnam deepened, he went to Saigon in 1965 to evaluate civilian pacification programs. He joined Maj. Gen. Edward G. Lansdale, the counterinsurgency expert, and for 18 months accompanied combat patrols into the jungles and villages.

A Grim Realization

What he saw began his transformation. It went beyond the failure to win the hearts and minds of the South Vietnamese. It was a mounting toll of civilian deaths, tortured prisoners and burned villages, a litany of brutality entered in military field reports as “clear and hold operations.”

“I saw it was all very hard on those people,” he told the syndicated columnist Mary McGrory. “But I told myself that living under communism would be harder, and World War III, which I thought we were preventing, would be worse.”

To Mr. McNamara, Mr. Ellsberg forecast a dismal prospect of continued death and destruction, ending perhaps in an American withdrawal and victory for North Vietnam. His reports went nowhere. But Mr. McNamara summoned him in 1967, with 35 others, to compile a history of the Vietnam conflict.

His contribution to the study was relatively modest. But he was deeply disturbed by its sweeping conclusions: that successive presidents had widened the war while concealing the facts from Congress and the American people. In 1968, Mr. Ellsberg returned to RAND, but began quietly acting on his changing views, composing war policy statements for Senator Robert F. Kennedy’s presidential race and attending antiwar conferences.