WASHINGTON (CNN) -- The Pentagon made public Sunday a memorandum it sent to supporters and critics of Donald Rumsfeld, after a week in which several retired generals called for the defense secretary's resignation.

The memo is an apparent attempt to challenge accusations that Rumsfeld has not adequately considered the views of U.S. military leaders in formulating decisions.

"The U.S. senior military leaders are involved to an unprecedented degree in every decision-making process in the Department of Defense," the first line of the memo said.

Entitled "U.S. Military Leaders and their Involvement in National Security Decision-Making," its existence was first reported in Sunday editions of the New York Times.

The one-page memo, which bears no date and no indication of who wrote it, said Rumsfeld met 139 times with the Joint Chiefs of Staff and 208 times with combatant commanders since the beginning of 2005.

The memo came after six retired generals in recent days publicly stated their criticism of Rumsfeld's leadership and called for his resignation. Retired Gen. Richard Myers, former chairman of the Joint Chiefs of Staff, said the retired generals' criticism is "inappropriate, because it's not the military that judges our civilian bosses."

He rejected suggestions that the joints chiefs had been intimidated by Rumsfeld and President Bush. "I absolutely disagree with that, of course. I mean, we gave him our best military advice," he told ABC's "This Week." "That's what we're obligated to do. If we don't do that, we should be shot." He added, "In our system, the civilian control of the military means that civilians make the decisions ... and we live by those decisions."

Myers also defended former Army Chief of Staff Gen. Eric Shinseki, who drew the Pentagon's ire when he told Congress in February 2003 that "something on the order of several hundred thousand soldiers" would be needed to govern Iraq after a war.

Rumsfeld, who advocated a smaller force, discounted that estimate within days.

Shinseki, who retired in June 2003, "was inappropriately criticized, I believe, for speaking out," Myers said. He added, however, that Shinseki's estimates "never came up" in meetings of the Joint Chiefs of Staff. Rumsfeld also drew support from retired Lt. Gen. Michael DeLong, the former deputy chief of U.S. forces in the Middle East. Writing in The New York Times, DeLong said the generals were wrong to blame Rumsfeld for the problems the United States now faces in Iraq -- "and when they do so in a time of war, the rest of the world watches."

"Mr. Rumsfeld does not give in easily in disagreements, either, and he will always force you to argue your point thoroughly. This can be tough for some people to deal with," DeLong wrote.

"I witnessed many heated but professional conversations between my immediate commander, Gen. Tommy Franks, and Mr. Rumsfeld -- but the secretary always deferred to the general on war-fighting issues." On the Sunday news shows, Rumsfeld received the support of some GOP politicians, while Democrats continued to call for his resignation.