At the same time, the escalating demand for protection has drawn security companies and personnel with questionable levels of training to the country and has led some contractors to arm themselves with guns purchased on the black market, contractors and security specialists say.
Without special diplomatic agreements in place, a U.S. civilian who is accused of mishandling a weapon or killing or injuring an Iraqi civilian might be subject to an Iraqi justice system.
"They're not members of the U.S. military or governed by the code of conduct, but they're civilians operating in a combat zone ... an inherent disconnect," said P.W. Singer, a military analyst at the Brookings Institution and author of Corporate Warriors - The Rise of the Privatized Military.
"What happens if they get in a firefight and something goes wrong and they get captured? We're in a sense making up the rules as we go along, and that's not a recipe for good policy."
Before yesterday's blast that leveled the Mount Lebanon Hotel in Baghdad, at least 20 foreign contractors had been killed in Iraq since major hostilities were declared at an end by President Bush last May 1, along with a number of Iraqis working for contractors, according to published reports.
No one formally tracks civilian deaths and injuries.
On Monday, four unarmed Southern Baptist missionaries were shot to death in Mosul when their car was ambushed.
On Tuesday, a German national and a Dutch national working on a water purification project were killed near Hillah, south of Baghdad. Their driver and a security guard also died.
On March 9, two American civilians working for the U.S. occupation authority were killed after several gunmen stopped their vehicle at a makeshift checkpoint south of Baghdad. Four men arrested in the killings were members of the new American-trained Iraqi police force, U.S. officials said.
"Clearly, there has been a shift in the insurgency and the way the extremists are conducting operations," Army Lt. Gen. Ricardo Sanchez, the highest-ranking commander in Iraq, said at a military ceremony Tuesday, pointing to the rash of civilian deaths.
"It is very clear they are going after these targets that might create some splits within the coalition."
This is a far different situation from that predicted by the government in the days leading up to the war.
"My belief is we will, in fact, be greeted as liberators," Vice President Dick Cheney said then.
A year later, in response to escalating attacks on civilians, and with $10 billion in new Iraq contracts being awarded this month, the Pentagon is soliciting bids for private security forces to protect its 10 prime U.S. contractors and their subcontractors.
Currently, contractors working in Iraq are responsible for their own security. The large companies, such as KBR - Halliburton's construction wing - and Bechtel, typically hire security firms that bring their own weapons. Many forbid or discourage their workers who are not employed as guards from carrying firearms.
Regulations set by the U.S.-led Coalition Provisional Authority say these civilians must receive special approval to carry a gun and have it licensed.
In such cases, the military is supposed to issue the gun and provide training, said Alan Chvotkin, senior vice president of the Professional Services Council, a trade organization representing contractors who sell services to the Pentagon and other agencies.
But the regulations have not been strictly enforced, and some contract workers - a good share of whom are retired from the military - choose to arm themselves with guns purchased on the black market, which are plentiful but often unreliable.
"The practical limitation is that the U.S. military doesn't have a lot of extra guns lying around," Chvotkin said. "I understand there's a lot of firepower in Iraq of all kinds. With the knowledge of the military or without, a lot of individuals are carrying pistols."
They're doing so because convoys are regularly coming under attack, often by insurgents who plant roadside explosives that can be detonated with remote devices, sometimes by snipers waiting for convoys with as many as 1,000 trucks and only a few Humvees providing security.
Meanwhile, contractors and researchers who study the military say they're concerned about the caliber of some of the guards employed by security companies streaming into Iraq.
Some of the companies, such as Dyncorp International, Kroll and Global Risks Strategies, have been doing this sort of work for years. But the industry has experienced huge growth since the 1990s with the increased outsourcing of work historically done by soldiers, and now it generates $100 billion in annual revenue worldwide, said Singer of the Brookings Institution.
The expanding market for these services has attracted hired guns and danger-seekers to war zones.
"We'd like to see better vetting of both companies and individuals," said Doug Brooks, president of the International Peace Operations Association, which represents security contractors who work abroad. "Some people are not qualified to be doing security. You do get some cowboys."
Deborah Avant, a political science professor at George Washington University who specializes in military change, said that if an active-duty member of the military kills a civilian, there are rules that define whether it was an appropriate action and the legal process for handling the case. When a private security person does the same thing, those rules don't apply.
"One of the things that's really problematic is these people aren't just walking around with billy clubs - they're walking around with AK-47s, so one of the issues is getting the rules of engagement straight," she said.
No one keeps track of the number of civilian guards working in Iraq, but the figure is estimated in the thousands. Many of them are retired military and law enforcement officers earning two to 10 times their former salaries.
Global Risks Strategies, one of the bigger contractors, says it has 1,100 employees in Iraq: 100 British former SAS troops, 500 Nepalese soldiers and 500 soldiers from Fiji.
"There's a feeling that if you use private companies it's not as provocative as if you use soldiers," said Bill Hartung, senior fellow at the World Policy Institute, who is doing research on the role of private contractors in Iraq and the war on terror.
"But the guy from Dyncorp swaggering around with a gun is just as identifiable as a symbol of American power as the military. They can be just as provocative, and on the flip side they're not as accountable. It raises the question, have we gone too far in our use of these companies?"
No one envisioned the magnitude of the security force needed when Bush declared an end to hostilities last spring. Contractors accustomed to this sort of work took their cue from the Balkans, Afghanistan and West Africa, but as it turned out the threat level in Iraq far surpassed those cases.
"This is an unprecedented situation, where civilian contractors are inside an insurgent battlefield," said Mike Battles, principal of Custer Battles LLC., which provides security, logistics and support services to the military in Iraq.
"In every previous case ... there's been an active cessation of hostilities before the contracting firms came in."
As a result, the cost of security, which in Iraq amounts to about 10 percent of the cost of the reconstruction contracts, has increased 25 to 30 percent since the first contractors landed there last spring, Battles said.
That's partly because the violence has shifted from random looting to ideologically driven attacks. Another factor is wage inflation: the danger and the pressing demand for guards have made private security a sellers' market.
"What it cost to hire qualified security personnel in June is a fraction of what it costs today," Battles said.
In Bechtel's original contract of $680 million, $500,000 was budgeted for security, primarily for radio communications. "It wasn't so much a security issue of the type we have now. It was more an issue of safety in case a car broke down," said Francis Canavan, the public affairs manager for the Bechtel project in Bagdhad, which is working on repairing Iraq's infrastructure.
Canavan wouldn't say how much the company is paying now for security, just that it's much more than envisioned. Employees travel in armed convoys wherever they go.
The Washington Group International of Boise, Idaho, which is building power plants and transmission lines and refurbishing buildings, has more than 300 employees and subcontractors working in Iraq, a number of them Iraqis.
The company has stationed about twice as many security guards there as workers, largely because it has to guard a 400-kilometer stretch of transmission lines that have been repaired to make sure looters don't sabotage their work, said Jack Herrmann, vice president for corporate communications.
Two Korean subcontractors for the Washington Group were killed in an ambush in November.
The Huntsville Army Corps of Engineers, which has seven contracts for detecting, capturing and destroying enemy munitions, estimates that 30 to 50 percent of the cost at its project sites is security-related.
"This is the most challenging environment we've ever worked in," said Robert Band, president and chief executive officer of the Perini Corp. of Framingham, Mass, which is helping to restore power generation and transmission. "And we've worked in the most violent locations, including Angola, Haiti, Nigeria, Liberia and Afghanistan."
The proliferation of unregulated guns makes some contractors nervous.
Privately, some say that unless there is a status-of-forces agreement that protects them diplomatically, they might pull out of Iraq when the United States hands over control to the Iraqis in June.
Brian J. Boquist, of International Charter Incorporated of Oregon - which provides helicopters and logistics support to the military - wrote in an e-mail that security firms working in Iraq are not protected, as they are elsewhere, by a government with diplomatic status and are not legally protected by a status-of-forces agreement.
"In Iraq it is the wild west," wrote Boquist, who served in Iraq as a senior military officer with special operations. "The security firms are covered by none of the above, and almost none of them have any real experience in war zones. For those reasons, we have stayed out of the place as it disintegrates from an insurgency to a civil war."