A federal oversight agency said today that the cost of things like housing employees, processing paperwork and providing security has consumed as much as 55 percent of the entire budget for some reconstruction projects in Iraq, vastly reducing the amount of money available for actual construction.

In fact, according to a report by the agency, the Special Inspector General for Iraq Reconstruction, those administrative and overhead costs, as they are known, may be claiming an even larger share of the money — but the government does not keep proper track of how the $18.4 billion of American taxpayer-financed reconstruction money approved by Congress two years ago is being spent.

Administration and overhead costs rarely claim more than a few percent of the budget for comparable construction projects in the United States.

The inspector general found that overhead costs varied widely over a sampling of contracts in Iraq that auditors examined, with some companies spending less than 20 percent on overhead while others spent more than half the project’s budget that way.

The highest overhead costs were found in the hundreds of millions of dollars worth of contracts awarded to KBR, the Halliburton subsidiary formerly known as Kellogg, Brown and Root, for the reconstruction of oil facilities in Iraq.

The report did not explain why KBR’s overhead costs under those contracts were more than 10 percentage points greater than any other contractor that was audited. KBR did not immediately respond to a request for comment on the findings.

In Iraq, where construction materials are scarce and contractors are forced to provide security for work sites and housing for Western employees, officials have said in the past that overhead costs were likely to be higher than normal; the early estimates were for at least 10 percent.

Western contractors and the American-led occupation authorities in Iraq have grudgingly conceded that the true overhead costs have turned out to be much higher than that figure. But the inspector general’s report is the first official estimate that more than half the total spent on some projects has gone to overhead instead of construction.

The conclusions were drawn from $1.3 billion in contracts for which United States government actually made an effort to track overhead costs, out of the total of $18.4 billion set aside for reconstruction in specific supplemental funding bill for the 2006 fiscal year.

The report concluded that a major reason for the enormous overhead costs was delay in starting reconstruction work after the United States ordered the contractors to "mobilize" in Iraq — meaning sending their employees and equipment there.

On some projects, the delay between mobilization and the start of construction was as long as nine months, the report said.

"The government blew the whistle for these guys to go to Iraq, and the meter ran," said Jim Mitchell, a spokesman for the inspector general’s office. "The government was billed for, sometimes, nine months before work began."

Mr. Mitchell said that in many cases the government did not begin tracking overhead costs for months after the companies mobilized, so that even the 55 percent overhead figure for some projects could be an underestimate.