There are two coalition armies in Iraq: the official one, which fights the war, and the private one, which supports it.

This latter group of civilians drives dangerous truck convoys, cooks soldiers' meals, and guards facilities and important officials. They rival in size the US military force there, and thousands have become casualties of the conflict. If this experience is any indication, they may change the makeup of US military forces in future wars.

Having civilians working in war zones is as old as war itself. But starting with US military action in the Balkans and Colombia in the mid-1990s and accelerating rapidly in Afghanistan and Iraq, the number and activity of contractors has greatly increased. Coming from dozens of countries, hired by hundreds of companies, contractors have seen their numbers rise faster than the Pentagon's ability to track them.

Now, the challenges of this privatization strategy are becoming clear.

Everything from who controls their activities to who cares for them when wounded remains unresolved, say experts in and out of the military. This has led to protests from families in the United States as well as concerns in military ranks about how contractors fit into the chain of command.

"This is a very murky legal space, and simply put we haven't dealt with the fundamental issues," says Peter Singer, a foreign policy specialist at the Brookings Institution in Washington. "What is their specific role, what is their specific status, and what is the system of accountability? We've sort of dodged these questions."

As the inevitable drawdown of US military forces in Iraq occurs, the importance of civilian workers there is likely to grow.

"In my view, the role of contractors is just going to continue to escalate, probably at an ever-increasing rate," says Deborah Avant, a political scientist at the University of California, Irvine, whose research has focused on civil-military relations.

For example, the new US Embassy now being completed in Baghdad – 21 buildings on 104 acres, an area six times larger than the United Nations complex in New York – is likely to be a permanent fixture needing hundreds if not thousands of civilian contractors to maintain it and provide services.

In Iraq, up to 180,000 contractors

Estimates of the number of private security personnel and other civilian contractors in Iraq today range from 126,000 to 180,000 – nearly as many, if not more than, the number of Americans in uniform there. Most are not Americans. They come from Fiji, Brazil, Scotland, Croatia, Hungary, New Zealand, Pakistan, South Africa, Australia, and other countries.

"A very large part of the total force is not in uniform," Scott Horton, who teaches the law of armed conflict at Columbia University School of Law, said in congressional testimony last month. In World War II and the Korean War, contractors amounted to 3 to 5 percent of the total force deployed. Through the Vietnam War and the first Gulf War, the percentage grew to roughly 10 percent, he notes. "But in the current conflict, the number appears to be climbing steadily closer to parity" with military personnel. "This represents an extremely radical transformation in the force configuration," he says.

Until recently, there has been little oversight of civilian contractors operating in Iraq. The Defense Department is not adequately keeping track of contractors – where they are or even how many there are, the Government Accountability Office concluded in a report last December. This is especially true as military units rotate in and out of the war zone (as do contractors) and institutional memory is lost.

This lack of accountability has begun to change with a Democrat-controlled Congress. As part of the 2007 National Defense Authorization Act passed last year, Congress now requires that civilian contractors who break the law – hurt or kill civilians, for example – come under the legal authority of the Uniform Code of Military Justice. So far, however, the Pentagon has not issued guidance to field commanders on how to do this.

Proposed bills in the House and Senate would require "transparency and accountability in military and security contracting." For example, companies would be required to provide information on the hiring and training of civilian workers, and the chairman of the Joint Chiefs of Staff would have to issue rules of engagement regarding the circumstances under which contractors could use force.

Senior commanders acknowledge the value of contractors, especially those that are armed and ready to fight if attacked.

At his Senate confirmation hearing in January, Army Gen. David Petraeus, commander of the multinational force in Iraq, said that the "surge" by US forces in Iraq might not include enough American troops. "However, there are tens of thousands of contract security forces and [Iraqi] ministerial security forces that do, in fact, guard facilities and secure institutions," he added. "That does give me the reason to believe that we can accomplish the mission in Baghdad."

Still, many senior military officers worry about the impact that relying on so many civilian contractors – especially armed private security forces – will have on the conduct of future conflicts. This past Christmas Eve, for example, a Blackwater USA contractor shot and killed an Iraqi security guard. The contractor was fired and returned to the US. The FBI and Justice Department are investigating.

The US military needs to take "a real hard look at security contractors on future battlefields and figure out a way to get a handle on them so that they can be better integrated – if we're going to allow them to be used in the first place," Col. Peter Mansoor, a deputy to General Petraeus, recently told Jane's Defence Weekly.

"I meet with a lot of O-5s and O-6s [lieutenant colonels and colonels] at the war colleges, and you hear a lot of that discomfort with how far it's gone," says Mr. Singer of Brookings.

Opinions differ over whether the trend in using more contractors is here to stay.

"Every war is unique, but the heavy use of private contractors in Iraq and Afghanistan is likely to persist in future conflicts," says military analyst Loren Thompson of the Lexington Institute in Arlington, Va. "Relying on market sources is intrinsically more flexible than using government workers, and nobody seriously believes that the market will fail to respond to multibillion dollar opportunities even when danger is involved."

"In addition," says Dr. Thompson, "modern military technology often requires support that only the original makers can provide."

A new military-industrial complex?

Other observers also foresee an increase in military contractors – for darker reasons.

The "military-industrial complex" that former President Eisenhower warned of has been overshadowed by the "war-service industry," says Dina Rasor, coauthor of the recent book "Betraying Our Troops: The Destructive Results of Privatizing War." The complex relied on the cold war to keep its budgets high, knowing that the weapons it produced probably would never be used. The war-service industry, by contrast, "doesn't build weapons but has to have a hot war or an occupation going on in order to keep its budgets high," says Ms. Rasor. Constituencies will be built within the military and in Congress to promote this growing industry, she predicts.

Lawrence Korb, a former assistant secretary of Defense, takes a different view. He predicts that the number of contractors providing military logistics support will shrink, in part because the US effort in Iraq will wind down at some point and in part because the US plans to increase the armed forces by 92,000 soldiers and marines over the next five years.

Looking ahead to the need for peacekeeping and stabilization in future conflicts, Dr. Korb says, "I can't imagine doing it again without thinking it through."

After trials of war, a lone helping hand in the US

Contrary to popular perception, most contractors are not the beefy, grim guys wearing scary sunglasses and carrying guns. But in a war like Iraq, every one from mechanics to translators has become a target. At least 916 contractors have been killed in the four-year war and more than 12,000 wounded, according to official statistics and Labor Department figures provided to the New York Times and Reuters. An unknown number experience symptoms of post-traumatic stress disorder (PTSD).

But unless they have previous military service, contractors are not eligible for help from the US Department of Veterans Affairs. Many have been denied treatment by insurance companies. In some cases, the companies they worked for have successfully fought legal efforts to declare the firms liable for physical or mental injury resulting from work in Iraq.

Enter Jana Crowder, a "stay-at-home mom with four kids" who started a website for moral support during the seven months her husband was an engineering contractor in Iraq.

"I had no idea what I was getting into," says Mrs. Crowder, who lives in Knoxville, Tenn. "I found a whole different war zone out there – contractors coming home physically and mentally damaged. I didn't even know what PTSD was, but I had guys calling me up saying they had nightmares, that they couldn't sleep, that they were hallucinating and crying."

Today, through her website (www.americancontractorsiniraq.com), Crowder is a liaison between troubled contractors and those who can help them. She organizes conferences and guides contractors through the bureaucratic and legal maze they face in filing workers' compensation claims.

As Congress and government agencies look deeper into the use of US military contractors in Iraq and Afghanistan, the families and supporters of civilian workers in the war zones are hopeful that their loved ones will get more and better treatment – especially for the mental and emotional shocks that remain.

Says Crowder, who's grateful that her husband came home in good shape: "PTSD doesn't know whether you're wearing a uniform or not."