In sharp contrast to his much-praised performance during the war in Afghanistan a year and a half ago, Defense Secretary Donald H. Rumsfeld has spent the last few days of the war in Iraq in a defensive posture, responding to criticism from current and former Army officers that the invasion began with too light a force on the ground.

The criticism clearly touched a nerve yesterday as Rumsfeld and Gen. Richard B. Myers, chairman of the Joint Chiefs of Staff, fielded a barrage of questions about the size of the force and the extent to which Rumsfeld shaped its deployment with unusual emotion, at unusual length.

Myers, usually reserved, unexpansive in his answers and highly deferential to Rumsfeld, launched into a thousand-word retort on his boss's behalf in which he questioned the critics' motives -- even their loyalty -- and said their charges have been "harmful to our troops that are out there fighting very bravely, very courageously."

Rumsfeld, as he has since the criticism began surfacing last week, insisted that the war plan belonged to his battlefield commander, Gen. Tommy R. Franks, head of the U.S. Central Command.

"I keep getting credit for it in the press, but the truth is, I would be happy to take credit for it but I can't," Rumsfeld said at a Pentagon news conference. "It was not my plan, it was General Franks's plan, and it was a plan that evolved over a sustained period of time, which I am convinced is an excellent plan."

But, to a very great extent, Rumsfeld is the force behind Franks's innovative -- and risky -- plan, a point the defense secretary's confidants, aides and admirers were only too happy to make before the war began and for the first few days of the invasion. It was Rumsfeld, they said, who pushed Franks for months to fashion a campaign premised on the synergy of disorienting air power, faster-moving ground forces, information dominance on the "digital battlefield" and greater reliance on Special Forces.

Those qualities bear Rumsfeld's indelible signature. They are reflected in the congressionally mandated Quadrennial Defense Review produced by his staff in the fall of 2001, and they are the priorities in his much heralded agenda for "transforming" a Cold War military to fight 21st century wars.

And when all the back and forth between Rumsfeld and Franks was said and done late last year, those characteristics were the essence of the plan the Bush administration believed had the potential for swiftly toppling Iraqi President Saddam Hussein's government.

Pushed by reporters on the subject yesterday, Rumsfeld admitted as much. "Nobody should go out of here with any idea that I or anyone else are distancing themselves from that plan, because I am not," Rumsfeld said. "I think Tom Franks is doing a superb job. The truth of the matter is, however, it was a long, iterative process. . . .

"Sure, did we have a voice in it? Did we have a part in fashioning it? You bet."

Another truth of the matter, to borrow Rumsfeld's phrase, is that the plan may turn out to be brilliant after all. The war is less than two weeks old; U.S. and British casualties have been relatively light; the advance to the outskirts of Baghdad has been swift; the Iraqi military has few options; and even its harassing tactics have come at enormous price in Iraqi lives and lost equipment.

"On balance," said Loren B. Thompson, a military analyst at the Lexington Institute, an Arlington think tank, "he's probably going to be vindicated."

And it must be remembered, Thompson said, that Rumsfeld, too, wanted a heavier force and would have had the 4th Infantry Division with its 25,000 soldiers and hundreds of tanks bearing down on Baghdad from the north had Turkey not refused to allow the northern front to be launched from its soil.

But numerous other analysts inside and outside the military say it is hard to deny that several key assumptions underlying the plan -- that the Iraqi military would not fight hard in the south, that the Iraqi government could be knocked off its feet by a precision blast of U.S. air power, and that the Iraqi people would rise up and greet U.S. and British forces as liberators -- did not immediately come to pass.

And since that is the case, they say, it is also hard to deny that more ground forces to protect vulnerable supply lines and root out the paramilitary fighters of Saddam's Fedayeen in key southern cities would have been enormously helpful thus far.

"No military professional looking at this objectively could argue that we had an adequate number of troops on the ground," said retired Army Lt. Col. Ralph Peters, a military analyst and author. "If Tommy Franks had had a free hand, this is not the plan he would have come up with. There wasn't a debate -- there was an argument. And the civilians [in Rumsfeld's office] had the upper hand."

To an extent, Peters said, Rumsfeld is paying a price for the way he has treated the Army, which -- rightly or wrongly -- has come to believe that the defense secretary is an air power advocate who is disdainful of heavy armored forces as relics of the past. And to an extent, Peters and others say, Rumsfeld is paying a price for what many in uniform perceive to be his lack of trust in their judgment.

But more than anything else, Peters said, Rumsfeld has become a lightning rod for criticism because he has not been frank with the public about the flawed assumptions and level of force that was on hand at the start of the war as a result.

"Rumsfeld is obviously brilliant, talented and driven, but his vanity is such that he can never admit when he's wrong," Peters said. "The war is going wonderfully. The performance is just remarkable by any standards. But it's not going according to plan."