“If this country has been misled, if this committee, this Congress, has been misled by pretext into a war in which thousands of young men have died, and many more thousands have been crippled for life, and out of which their country has lost prestige, moral position in the world, the consequences are very great,” Senator Albert Gore Sr. of Tennessee, the father of the future vice president, said in March 1968 in a closed session of the Foreign Relations Committee.

The documents are Volume 20 in a regular series of releases of historical transcripts from the committee, which conducted most of its business in executive session during the 1960s, before the Senate required committee meetings to be public. The documents were edited by Donald Ritchie, the Senate historian, and cover 1968, when members of the committee were anguished over Vietnam and in a deteriorating relationship with the Johnson White House over the war.

Historians said the transcripts, which are filled with venting by the senators about the Johnson administration and frustrations over their own ineffectiveness, added little new to the historical record. Even at the time, there was widespread skepticism about the Gulf of Tonkin incident, in which the North Vietnamese were said to have attacked American destroyers on Aug. 4, 1964, two days after an earlier clash.

President Lyndon B. Johnson cited the attacks to persuade Congress to authorize broad military action in Vietnam, but historians in recent years have concluded that the Aug. 4 attack never happened.

Still, the transcripts show the outrage the senators were expressing behind closed doors. “In a democracy you cannot expect the people, whose sons are being killed and who will be killed, to exercise their judgment if the truth is concealed from them,” Senator Frank Church, Democrat of Idaho, said in an executive session in February 1968.

But the senators also worried that releasing a committee staff investigation that raised doubts about the Tonkin incident would only inflame the country more. As Senator Mike Mansfield, Democrat of Montana, put it, “You will give people who are not interested in facts a chance to exploit them and to magnify them out of all proportion.”

At another point, the committee’s chairman, Senator William Fulbright, Democrat of Arkansas, raised concerns that if the senators did not take a stand on the war, “We are just a useless appendix on the governmental structure.”

The current chairman of the committee, Senator John Kerry, Democrat of Massachusetts, said Wednesday in an interview that the transcripts were especially revealing to him. In February 1968, when some of the most intense debates of the committee were occurring, Mr. Kerry was on a ship headed for Vietnam.

The release of documents, he said, “shows these guys wrestling with the complexity of it when our generation was living it out in a very personal way.”

He continued, “You couldn’t have imagined in that room of the Capitol that policy makers were agonizing over it in that way, and having that gut kind of conversation.”

In the end, however, the senators did not further pursue their doubts. As Mr. Church said in one session that was focused on the staff report into the episode, if the committee came up with proof that an attack never occurred, “we have a case that will discredit the military in the United States, and discredit and quite possibly destroy the president.”

He added that unless the committee had the evidence to substantiate the charges, “The big forces in this country that have most of the influence and run most of the newspapers and are oriented toward the presidency will lose no opportunity to thoroughly discredit this committee.”

Robert J. Hanyok, a National Security Agency historian, said Wednesday in an interview that “there were doubts, but nobody wanted to follow up on the doubts,” perhaps because “they felt they’d gone too far down the road.”

Mr. Hanyok concluded in 2001 that N.S.A. officers had deliberately falsified intercepted communications in the incident to make it look like the attack on Aug. 4, 1964, had occurred, although he said they acted not out of political motives but to cover up earlier errors.

Many historians say that President Johnson might have found reason to escalate military action against North Vietnam even without the Tonkin Gulf crisis, and that he apparently had his own doubts. Historians note that a few days after the supposed attack he told George W. Ball, the under secretary of state, “Hell, those dumb, stupid sailors were just shooting at flying fish!”