By DAVID S. CLOUD and ERIC SCHMITT
WASHINGTON, April 13 — The widening circle of retired generals who have stepped forward to call for Defense Secretary Donald H. Rumsfeld's resignation is shaping up as an unusual outcry that could pose a significant challenge to Mr. Rumsfeld's leadership, current and former generals said on Thursday.
Maj. Gen. Charles H. Swannack Jr., who led troops on the ground in Iraq as recently as 2004 as the commander of the Army's 82nd Airborne Division, on Thursday became the fifth retired senior general in recent days to call publicly for Mr. Rumsfeld's ouster. Also Thursday, another retired Army general, Maj. Gen. John Riggs, joined in the fray.
"We need to continue to fight the global war on terror and keep it off our shores," General Swannack said in a telephone interview. "But I do not believe Secretary Rumsfeld is the right person to fight that war based on his absolute failures in managing the war against Saddam in Iraq."
Another former Army commander in Iraq, Maj. Gen. John Batiste, who led the First Infantry Division, publicly broke ranks with Mr. Rumsfeld on Wednesday. Mr. Rumsfeld long ago became a magnet for political attacks. But the current uproar is significant because Mr. Rumsfeld's critics include generals who were involved in the invasion and occupation of Iraq under the defense secretary's leadership.
There were indications on Thursday that the concern about Mr. Rumsfeld, rooted in years of pent-up anger about his handling of the war, was sweeping aside the reticence of retired generals who took part in the Iraq war to criticize an enterprise in which they participated. Current and former officers said they were unaware of any organized campaign to seek Mr. Rumsfeld's ouster, but they described a blizzard of telephone calls and e-mail messages as retired generals critical of Mr. Rumsfeld weighed the pros and cons of joining in the condemnation.
Even as some of their retired colleagues spoke out publicly about Mr. Rumsfeld, other senior officers, retired and active alike, had to be promised anonymity before they would discuss their own views of why the criticism of him was mounting. Some were concerned about what would happen to them if they spoke openly, others about damage to the military that might result from amplifying the debate, and some about talking outside of channels, which in military circles is often viewed as inappropriate.
The White House has dismissed the criticism, saying it merely reflects tensions over the war in Iraq. There was no indication that Mr. Rumsfeld was considering resigning.
"The president believes Secretary Rumsfeld is doing a very fine job during a challenging period in our nation's history," the White House spokesman, Scott McClellan, told reporters on Thursday.
Among the retired generals who have called for Mr. Rumsfeld's ouster, some have emphasized that they still believe it was right for the United States to invade Iraq. But a common thread in their complaints has been an assertion that Mr. Rumsfeld and his aides too often inserted themselves unnecessarily into military decisionmaking, often disregarding advice from military commanders.
The outcry also appears based in part on a coalescing of concern about the toll that the war is taking on American armed forces, with little sign, three years after the invasion, that United States troops will be able to withdraw in large numbers anytime soon.
Pentagon officials, while acknowledging that Mr. Rumsfeld's forceful style has sometimes ruffled his military subordinates, played down the idea that he was overriding the advice of his military commanders or ignoring their views.
His interaction with military commanders has "been frequent," said Lawrence Di Rita, a top aide to Mr. Rumsfeld.
"It's been intense," Mr. Di Rita said, "but always there's been ample opportunity for military judgment to be applied against the policies of the United States."
Some retired officers, however, said they believed the momentum was turning against Mr. Rumsfeld.
"Are the floodgates opening?" asked one retired Army general, who drew a connection between the complaints and the fact that President Bush's second term ends in less than three years. "The tide is changing, and folks are seeing the end of this administration."
No active duty officers have joined the call for Mr. Rumsfeld's resignation. In interviews, some currently serving general officers expressed discomfort with the campaign against Mr. Rumsfeld, which has been spearheaded by, among others, Gen. Anthony C. Zinni, who headed the United States Central Command in the late 1990's before retiring from the Marine Corps. Some of the currently serving officers said they feared the debate risked politicizing the military and undercutting its professional ethos.
Some say privately they disagree with aspects of the Bush administration's handling of the war. But many currently serving officers, regardless of their views, say respect for civilian control of the military requires that they air differences of opinion in private and stay silent in public.
"I support my secretary of defense," Lt. General John Vines, who commands the Army's 18th Airborne Corps, said when questioned after a speech in Washington on Thursday about the calls for Mr. Rumsfeld to step down. "If I publicly disagree with my civilian leadership, I think I've got to resign. My advice should be private."
Some of the tensions between Mr. Rumsfeld and the uniformed military services date back to his arrival at the Pentagon in early 2001. Mr. Rumsfeld's assertion of greater civilian control over the military and his calls for a slimmer, faster force were viewed with mistrust by many senior officers, while his aggressive, sometimes abrasive style also earned him enmity.
Mr. Rumsfeld's critics often point to his treatment of Gen. Eric Shinseki, then the Army chief of staff, who told Congress a month before the 2003 invasion of Iraq that occupying the country could require "several hundred thousand troops," rather than the smaller force that was later provided. General Shinseki's estimate was publicly dismissed by Pentagon officials.
"Rumsfeld has been contemptuous of the views of senior military officers since the day he walked in as secretary of defense. It's about time they got sick and tired," Thomas E. White, the former Army secretary, said in a telephone interview on Thursday. Mr. White was forced out of his job by Mr. Rumsfeld in April of 2003.
Lt. Gen. Gregory Newbold of the Marine Corps, who retired in late 2002, has said he regarded the American invasion of Iraq unnecessary. He issued his call for replacing Mr. Rumsfeld in an essay in the current edition of Time magazine. General Newbold said he regretted not opposing the invasion of Iraq more vigorously, and called the invasion peripheral to the job of defeating Al Qaeda.
General Swannack, by contrast, continues to support the invasion but said that Mr. Rumsfeld had micromanaged the war in Iraq, rather than leaving it to senior commanders there, including Gen. George W. Casey Jr. of the Army, the top American officer in Iraq, and Gen. John P. Abizaid of the Army, the top officer in the Middle East. "My belief is Rumsfeld does not really understand the dynamic of counterinsurgency warfare," General Swannack said.
The string of retired generals calling for Rumsfeld's removal has touched off a vigorous debate within the ranks of both active-duty and retired generals and admirals.
Some officers who have worked closely with Mr. Rumsfeld reject the idea that he is primarily to blame for the inability of American forces to defeat the insurgency in Iraq. One active-duty, four-star Army officer said he had not heard among his peers widespread criticism of Mr. Rumsfeld, and said he thought the criticism from his retired colleagues was off base. "They are entitled to their views, but I believe them to be wrong. And it is unfortunate they have allowed themselves to become in some respects, politicized."
Gen. Jack Keane, who was Army vice chief of staff in 2003 before retiring, said in the planning of the Iraq invasion, senior officers as much as the Pentagon's civilian leadership underestimated the threat of a long-term insurgency.
"There's shared responsibility here. I don't think you can blame the civilian leadership alone," he said.
Maj. Gen. Paul D. Eaton, a retired Army general, called for Mr. Rumsfeld's resignation in March.
The criticism of Mr. Rumsfeld may spring from multiple motives. General Zinni, for example, is in the middle of a tour promoting a new book critical of the Bush administration.
General Riggs, who called for Mr. Rumsfeld's resignation in an interview on Thursday with National Public Radio, left the Pentagon in 2004 after clashing with civilian leaders and then being investigated for potential misuse of contractor personnel.
But there were also signs that the spate of retired generals calling for Mr. Rumsfeld's departure was not finished. Lt. Gen. Paul Van Riper, who is retired from the Marine Corps, said in an interview Thursday he had received a telephone call from another retired general who was weighing whether to publicly join the calls for Mr. Rumsfeld's dismissal.
"He was conflicted, and when I hung up I didn't know which way he was going to go," General Van Riper said.
Thom Shanker contributed reporting for this article.