Washington ? Defense Secretary Donald Rumsfeld and his top military leader on Tuesday issued their strongest rebuttal to date of recent comments by retired generals criticizing Iraq war planning and calling on Rumsfeld to resign.

In particular, Rumsfeld said he didn’t recall retired Lt. Gen. Gregory Newbold raising any objections to the war planning when he was working in the Pentagon for the Joint Chiefs of Staff.

“He never raised an issue publicly or privately when he was here that I know of,” said Rumsfeld. “An awful lot of people around here were not shy about giving their views. … But in terms of why he would come up with this now, I just can’t speak to that.”

Rumsfeld said the criticism doesn’t affect his ability to do his job.

Newbold, in Time magazine, said he was outspoken in his criticism before the war, saying the “zealots’ rationale for war made no sense.” From 2000 until October 2002, Newbold served as director of operations for the Joint Chiefs. The U.S. invaded Iraq in March 2003.

At least two other retired generals have raised similar concerns in recent weeks about the administration’s war policies, including Gen. Anthony Zinni, former U.S. Mideast commander.

To date, President Bush has rejected calls for Rumsfeld to step down. The defense secretary has served in that job since shortly after Bush took office in 2001.

Gen. Peter Pace, chairman of the Joint Chiefs of Staff, said military leaders, during dozens of prewar meetings, laid out a number of questions and concerns about whether there were enough troops and resources for the invasion.

In the end, he said, “I was very comfortable with the prewar planning. I am comfortable with the way it was executed. And I would go back, given the same facts and figures, and reach the same conclusion.”

Asked whether the U.S. has the resources to fight the war in Iraq and another major conflict – such as a war in Iran – at the same time, Pace said there are about 2 million U.S. service members who are not in the Gulf region now.

“We have sufficient personnel, weapons, equipment, you name it, to handle any adversary that might come along,” he said.

In a fundraising speech Tuesday in Des Moines, Iowa, Bush said that he understands the war has meant difficult times for Americans but that the United States is not going to retreat.

“We’re not going to be intimidated by thugs and assassins,” Bush said. “We will achieve victory in Iraq. And by achieving victory in Iraq, we will make it more secure for a generation of Americans. They hope that we lose our nerve. We will not lose our nerve.”