The website’s “interactive timeline” omits the Fulbright hearings in the Senate, where in 1971 a disaffected young Vietnam veteran named John Kerry — now President Obama’s secretary of state — asked, “How do you ask a man to be the last man to die for a mistake?” In one early iteration, the website referred to the 1968 My Lai massacre, in which American troops killed hundreds of Vietnamese civilians, as the My Lai Incident.

The glossy view of history has now prompted more than 500 scholars, veterans and activists — including the civil rights leader Julian Bond; Daniel Ellsberg, who leaked the top-secret Pentagon Papers; Lawrence J. Korb, a former assistant secretary of defense under President Ronald Reagan; and Peter Yarrow of the folk trio Peter, Paul and Mary — to join Mr. Hayden in demanding the ability to correct the Pentagon’s version of history and a place for the old antiwar activists in the anniversary events.

This week, in a move that has drawn the battle lines all over again, the group sent a petition to Lt. Gen. Claude M. Kicklighter, the retired Vietnam veteran who is overseeing the commemoration, to ask that the effort not be a “one-sided” look at a war that tore a generation apart.

General Kicklighter declined to be interviewed, but a Pentagon spokesman, Lt. Col. Tom Crosson, said in an email that the mission of the commemoration, as directed by Congress, is to “assist a grateful nation” in thanking veterans and their families. He said that the Pentagon was willing to make corrections “when factual errors or potential mischaracterizations are brought to our attention,” and that “there is no attempt to whitewash the history of the Vietnam War.”

The team has already changed some facts: After Nick Turse, the author of a book on Vietnam, noted the My Lai Incident reference in a February article on the website TomDispatch, the language was revised to read, “Americal Division Kills Hundreds of Vietnamese Citizens at My Lai.” It still does not use the word massacre.