June 30, 1971 and staff at the New York Times look at a proof sheet of a page containing the secret Pentagon report on Vietnam(AP)

Forty years after the explosive leak of the Pentagon Papers, a secret government study chronicling deception and misadventure in US conduct of the Vietnam War, the report is being officially released.

The 7,000-page report was the WikiLeaks disclosure of its time, a sensational breach of government confidentiality that shook Richard Nixon's presidency and prompted a Supreme Court fight that advanced press freedom.

Prepared near the end of Lyndon Johnson's term by Defence Department and private foreign policy analysts, the report was leaked primarily by one of them, Daniel Ellsberg, in an act of defiance that stands as one of the most dramatic episodes of whistleblowing in US history.

The National Archives and presidential libraries are releasing the report in full, long after most of its secrets had spilled. The release is timed 40 years to the day after The New York Times published the first in its series of stories about the findings, on June 13, 1971. The papers showed that the Johnson, Kennedy and prior administrations had been escalating the conflict in Vietnam while misleading Congress, the public and allies.

As scholars pore over the 47-volume report, Mr Ellsberg says the chance of them finding great new revelations are slight. Most of it has come out in congressional forums and by other means, and he plucked out the best when he painstakingly photocopied pages that he spirited from a safe night after night, and returned in the mornings. He said the value in the official release was in having the entire study finally brought together and put online, giving today's generations ready access to it.

At the time, Nixon was delighted that people were reading about bumbling and lies by his predecessor, which he thought would take some anti-war heat off him. But if he loved the substance of the leak, he hated the leaker.

He called the leak an act of treachery and vowed that the people behind it "have to be put to the torch." He feared that Mr Ellsberg represented a left-wing cabal that would undermine his own administration with damaging disclosures if the government did not crush him and make him an example for all others with loose lips.

Nixon's attempt to avenge the Pentagon Papers leak failed. First the Supreme Court backed the Times, The Washington Post and others in the press and allowed them to continue publishing stories on the study in a landmark case for the First Amendment. Then the government's espionage and conspiracy prosecution of Mr Ellsberg and his colleague Anthony J. Russo Jr. fell apart, a mistrial declared because of government misconduct.

The judge threw out the case after agents of the White House broke into the office of Mr Ellsberg's psychiatrist to steal records in hopes of discrediting him, and after it surfaced that Ellsberg's phone had been tapped illegally. That September 1971 break-in was tied to the Plumbers, a shady White House operation formed after the Pentagon Papers disclosures to stop leaks, discredit Nixon's opponents and serve his political ends. The next year, the Plumbers were implicated in the break-in at the Democratic Party headquarters in the Watergate building.

PA