WASHINGTON, December 2 The US National Security Agency has released hundreds of pages of long-secret documents on the 1964 Gulf of Tonkin incident, which played a critical role in significantly expanding the American commitment to the Vietnam War.

The material, posted on the Internet overnight on Wednesday, included one of the largest collections of secret intercepted communications ever made available. The most provocative document is a 2001 article in which an agency historian argued that the agency’s intelligence officers “deliberately skewed” the evidence passed on to policy makers and the public to falsely suggest that North Vietnamese ships had attacked American destroyers on August 4, 1964.

Based on the assertion that such an attack had occurred, President Lyndon B. Johnson ordered airstrikes on North Vietnam and the US Congress passed a broad resolution authorising military action.

The historian, Robert J. Hanyok, wrote the article in an internal publication and it was classified top secret despite the fact that it dealt with events in 1964. Word of Hanyok’s findings leaked to historians outside the agency, who requested the article under the Freedom of Information Act in 2003.

Some intelligence officials said they believed the article’s release was delayed because the agency was wary of comparisons between the roles of flawed intelligence in the Vietnam War and in the war in Iraq.

In his 2001 article, an elaborate piece of detective work, Hanyok wrote that 90 per cent of the intercepts of North Vietnamese communications relevant to the supposed August 4, 1964, attack were omitted from the major agency documents going to policy makers.

“The overwhelming body of reports, if used, would have told the story that no attack had happened,” he wrote. “So a conscious effort ensued to demonstrate that an attack occurred.”