The Pentagon has defended Defence Secretary Donald Rumsfeld against charges there were not enough troops in Iraq at the time of the invasion.
Widespread looting broke out in Iraq as the regime crumbled
In a statement, it said Mr Rumsfeld took advice from military commanders when deciding on troop levels.
The statement responds to criticism from the former civilian administrator in Iraq, Paul Bremer.
On Monday, Mr Bremer said the US had paid a "big price" for having too few troops on the ground in May 2003.
In a speech reported by the Washington Post, he said he had arrived in Baghdad on 6 May 2003 to find "horrid" looting and an unstable situation.
"We paid a big price for not stopping it, because it
established an atmosphere of lawlessness... We never had enough troops on the ground," he said.
Mr Bremer later said he had supported the invasion, and only recognised the troop shortage with the benefit of hindsight. He added that he believed current troop numbers in Iraq were sufficient.
But the speech added to the woes of Mr Rumsfeld, who this week has also had to back-pedal on remarks in which he said he had found no "strong, hard evidence" linking former Iraqi President Saddam Hussein and Osama Bin Laden's al-Qaeda network.
In its statement, the Pentagon said Mr Rumsfeld "relied upon the recommendations of the military commanders... as the basis for decisions regarding force levels".
Paul Bremer was the chief US representative in Iraq
"Before, during, and subsequent to Mr Bremer's tenure", commanders believed the US had an appropriate level of forces, the statement says.
The statement says that while in Iraq, "Mr Bremer was understandably interested in - but not in charge of - security issues".
This looks like quite a put-down for Mr Bremer, says the BBC's Nick Childs at the Pentagon.
The release of a formal statement reflects the political fallout from Mr Bremer's comments, he adds.
Mr Bremer sought to qualify his original comments on Tuesday, when he told an audience in Michigan:
"One way to have stopped the looting would have been to have more troops on the ground.
"That's a retrospective wisdom of
mine, looking backward. I think there are enough troops
there now for the job we are doing."