Months after American combat troops settled into occupation duty, they were camped out in primitive, dust-blown shelters without windows or air conditioning. The Army has invested heavily in modular barracks, showers, bathroom facilities and field kitchens, but troops in Iraq were using ramshackle plywood latrines and living without fresh food or regular access to showers and telephones.

Even mail delivery -- also managed by civilian contractors -- fell weeks behind.

Though conditions have improved, the problems raise new concerns about the Pentagon's growing global reliance on defense contractors for everything from laundry service to combat training and aircraft maintenance. Civilians help operate Navy Aegis cruisers and Global Hawk, the high-tech robot spy plane.

Civilian contractors may work well enough in peacetime, critics say. But what about in a crisis?

"We thought we could depend on industry to perform these kinds of functions," Lt. Gen. Charles S. Mahan, the Army's logistics chief, said in an interview.

One thing became clear in Iraq. "You cannot order civilians into a war zone," said Linda K. Theis, an official at the Army's Field Support Command, which oversees some civilian logistics contracts. "People can sign up to that -- but they can also back out."

As a result, soldiers lived in the mud, then the heat and dust. Back home, a group of mothers organized a drive to buy and ship air conditioners to their sons. One Army captain asked a reporter to send a box of nails and screws to repair his living quarters and latrines.

For almost a decade, the military has been shifting its supply and support personnel into combat jobs and hiring defense contractors to do the rest. This shift has accelerated under relentless pressure from Defense Secretary Donald Rumsfeld to make the force lighter and more agile.

"It's a profound change in the way the military operates," said Peter W. Singer, author of a new book, "Corporate Warriors," a detailed study of civilian contractors. He estimates that over the past decade, there has been a ten-fold increase in the number of contract civilians performing work the military used to do itself.

"When you turn these services over to the private market, you lose a measure of control over them," said Singer, a foreign policy researcher at the Brookings Institution, a think tank in Washington.

Replacing 1,100 Marine cooks with civilians, as the Corps did two years ago, might make short-term economic sense.

But cooks might be needed as riflemen -- as they were during the desperate Battle of the Bulge in December 1944. And untrained civilians "can walk off the job any time they want, and the only thing the military can do is sue them later on," Singer said.

Thanks to overlapping contracts and multiple contracting offices, nobody in the Pentagon seems to know precisely how many contractors are responsible for which jobs -- or how much it all costs.

That's one reason the Bush administration can only estimate that it is spending about $4 billion a month on troops in Iraq. White House Budget Director Joshua Bolten said this week he could not even estimate the cost of keeping troops in Iraq in fiscal 2004, which begins Oct. 1.

Last fall the Army hired Kellogg Brown & Root, a Houston-based contractor, to draw up a plan for supporting U.S. troops in Iraq, covering everything from handling the dead to managing airports. KBR, as it's known, eventually received contracts to perform some of the jobs, and it and other contractors began assembling in Kuwait for the war.

But as the conflict approached, insurance rates for civilians skyrocketed -- to 300 percent to 400 percent above normal, according to Mike Klein, president of MMG Agency Inc., a New York insurance firm. Soldiers are insured through the military and rates don't rise in wartime.

It got "harder and harder to get (civilian contractors) to go in harm's way," said Mahan, the Army logistics chief.

The Army had $8 million in contracts for troop housing in Iraq sitting idle, Mahan said. "Our ability to move (away) from living in the mud is based on an expectation that we would have been able to go to more contractor logistical support early on," Mahan said.

Logistics support for troops in Iraq is handled by dozens of companies, each hired by different commands and military agencies with little apparent coordination or oversight.

Patrice Mingo, a spokesman for KBR, declined comment. Don Trautner, an Army official who manages a major logistics contract with KBR for troop support in Iraq, said he knew of "no hesitation or lateness" by KBR civilian contractors. "There were no delays I know of," he said, making clear that he did not speak for other contractors.