From his office across the street from the Fair Oaks mall in Fairfax County, Eugene C. Renzi oversees a couple of dozen ManTech International Corp. network engineers, software specialists and telecommunications experts at work in Turkey and Kuwait.

The workers, many of them retired from the military, have toiled for the past few months alongside U.S. soldiers, sailors and Marines.

 "We're right there in the field with the units. We're committed to support our armed forces," said Renzi, ManTech's executive vice president. "It takes more than the fighting force to win that war, more so now because of the complexity of the equipment, and that's where ManTech comes in."

Private contractors are sending thousands of technical experts to the Persian Gulf region. They operate communications systems, repair helicopters, fix weapons systems and link the computers with the troops to command centers.

Many of the defense and intelligence contractors are from the Washington area. Reston's DynCorp said it has about a thousand workers doing aircraft maintenance in Kuwait and security work in Qatar. Previously DynCorp repaired tanks and heavy equipment that were sent to the Middle East. Science Applications International Corp. of McLean said it has 150 employees in the Persian Gulf region but would not say what they are doing.

The consulting firm Booz Allen Hamilton Inc. has about 100 people in Saudi Arabia "helping the U.S. government figure how air base operations would work there," said C.G. Appleby, the McLean company's general counsel and senior vice president for risk management. A spokesman for defense contractor Lockheed Martin Corp. of Bethesda said company employees are working in the Middle East on weapons and computer systems.

CACI International Inc. chairman and chief executive J.P. "Jack" London said the computer-network services firm has "a meaningful presence" in Bahrain and "two or three other countries." He declined to say exactly how many employees the Arlington company has in the region.

"We're playing a role in a large choreography to make sure the president and [Defense Secretary Donald H.] Rumsfeld have the right information at the right time and can disseminate their decisions back to the battlefield," London said. "We'll be ahead of the enemy's ability to outmaneuver us."

The U.S. Central Command in Tampa, which is directing the troop buildup near Iraq, said it does not know how many U.S. companies have people in the Persian Gulf area or the number of workers they have sent there.

P.W. Singer of the Brookings Institution in Washington has studied the growth of private contractors in war zones. Based on civilian contractors' presence in the Balkans and more recently in Central Asia, Singer estimated that several hundred companies will send about 20,000 contractors to a war with Iraq, about one civilian for every 10 military personnel.

Singer, whose book "Corporate Warriors" is to be published in May, said such a sizable deployment of "privatized military firms" would be 10 times the size of their presence in the 1991 Persian Gulf War.

"The military would not be able to function without these people there," Singer said. "Everywhere U.S. forces are deployed, there's a contractor helping them out."

"Think of everything the Navy used to do" to move equipment to where a war might be fought, he said. "Now a company does it." Logistics, he said, is the heart of warfare, and much of it has been privatized.

"Now it extends to critical weapons," Singer said. Private companies help maintain the B-2 stealth bomber, attack helicopters and drone reconnaissance aircraft, he said.

Singer said that because the military has shrunk by a third in the past decade, civilians are needed to fill jobs that might once have gone to military personnel.

"In previous decades, a company like Northrop Grumman would build a system and hand it over to the military," Singer said. Now, private contractors maintain the equipment, he said.

Singer and two military historians, Wayne E. Lee of the University of Louisville and Allan R. Millett of Ohio State University, attributed the growth of the battlefront corporate presence chiefly to the heightened reliance on civilian technology adapted for military use.

"This is off-the-shelf technology rather than command-requested technology, modified to military use," Lee said. Then, he added, there is the need to keep the complex equipment operating properly, and "the maintenance of sophisticated technology and the level of expertise needed is not something the military teaches."

Technical-support contractors, Millett said, are often "folded right into the units."

But the increased use of civilian contractors is not without risk for the military, Singer said. They may be patriotic former military men and have security clearances, but they answer to their employers, not the armed forces. And the workers, who get 20 to 30 percent "danger pay" bonuses from their employers, may not properly calculate the risk to themselves until they come under fire.

Singer said that during the Persian Gulf War, "a very small number" of private contractors working at an air base in Saudi Arabia fled from fear that chemical weapons might be used.

"A soldier could never say, 'I don't want to go' " into battle, at least not without facing a court-martial, Singer said. "A contractor could and would just lose their job. It's one of those worries."

Renzi, of ManTech, said that is not plausible. He and other executives said they seek volunteers for Persian Gulf assignments, which can last three months to a year.

"We know the people who we've got with us," Renzi said of ManTech employees. "They know the dangers. No one is ordered to go."

Lockheed spokesman Thomas J. Jurkowsky said: "Sometimes civilian contractors are scoffed at. But they've got as much pride in their country as someone on active duty. As a defense contractor, we've probably got more retired military people than most companies. They've been overseas. They're used to working in that type of environment"

ManTech's chairman, chief executive and president, George J. Pedersen, said his employees are not armed but that the military has rules for protecting contractors. Employees have protective gear and took a 10-day training course at a Georgia military base on what to do if there is an attack with chemical or biological weapons.

The danger to civilians working in the Persian Gulf was made clear in late January when two contractors from Tapestry Solutions Inc., a San Diego firm hired by the Defense Department to install computer software, were ambushed in Kuwait. The company's co-founder, Michael Rene Pouliot, was killed and David J. Caraway, a software engineer, was wounded.

With that in mind, will the ManTech and CACI workers head into Iraq if warfare breaks out? It is a question their chief executives are reluctant to talk about.

"I don't know," Pedersen said. "We will go as far forward as contractors are allowed."

CACI's London said: "I'm not prepared to address that. There are no commitments right now. We'll have to assess that."