"Rather than come clean about their mistake, they helped launch the United States into a bloody war that would last for 10 years," Mr. Aid said.

Asked about Mr. Hanyok's research, an N.S.A. spokesman said the agency intended to release his 2001 article in late November. The spokesman, Don Weber, said the release had been "delayed in an effort to be consistent with our preferred practice of providing the public a more contextual perspective."

Mr. Weber said the agency was working to declassify not only Mr. Hanyok's article, but also the original intercepts and other raw material for his work, so the public could better assess his conclusions.

The intelligence official gave a different account. He said N.S.A. historians began pushing for public release in 2002, after Mr. Hanyok included his Tonkin Gulf findings in a 400-page, in-house history of the agency and Vietnam called "Spartans in Darkness." Though superiors initially expressed support for releasing it, the idea lost momentum as Iraq intelligence was being called into question, the official said.

Mr. Aid said he had heard from other intelligence officials the same explanation for the delay in releasing the report, though neither he nor the intelligence official knew how high up in the agency the issue was discussed. A spokesman for Gen. Michael V. Hayden, who was the agency's. director until last summer and is now the principal deputy director of national intelligence, referred questions to Mr. Weber, the N.S.A. spokesman, who said he had no further information.

Many historians believe that even without the Tonkin Gulf episode, Johnson might have found a reason to escalate military action against North Vietnam. They note that Johnson apparently had his own doubts about the Aug. 4 attack and that a few days later told George W. Ball, the under secretary of state, "Hell, those dumb, stupid sailors were just shooting at flying fish!"

But Robert S. McNamara, who as defense secretary played a central role in the Tonkin Gulf affair, said in an interview last week that he believed the intelligence reports had played a decisive role in the war's expansion.