Scores of illegal immigrants (search) working as cooks, laborers, janitors, even foreign-language instructors have been seized at military bases around the country in the past year, raising concerns in some quarters about security and troop safety.

The immigrants did not work directly for the military but for private contractors, as part of a large-scale effort by the Pentagon to outsource many routine rear-echelon jobs and free up the troops to concentrate on waging war.

Some worry that this fast-growing practice could make U.S. military installations more vulnerable to security breaches.

"We can't let down our guard," said Rep. Robin Hayes (search), a North Carolina Republican whose district includes Fort Bragg, home of the Army's Special Operations Command. "The motive of these particular individuals remains unclear. However, my greatest concern is that they were able to gain access to the installation at all."

Since the Sept. 11 attacks, immigration officials have focused on military bases as well as airports, nuclear power plants and the nation's power grid. In the past year, they have caught about 150 illegal immigrants at military installations around the country, said Jamie Zuieback, a spokeswoman for the Immigration and Customs Enforcement service in Washington.

There is no evidence any of them had any links to terrorists, though investigations are continuing, Zuieback said. She said the agency is concerned that such installations "could be vulnerable to exploitation by someone who has ill intent."

This month, officials arrested three foreign language instructors at Fort Bragg. Over the summer, authorities apprehended 74 construction workers lacking documentation at Camp Lejeune, the Marines' major base on the Atlantic Ocean, and caught 49 illegal immigrants at North Carolina's Seymour Johnson Air Force Base. Illegals have also been caught at bases in Idaho and Florida.

Some of them were deported; others were escorted off base and released.

The total of about 150 does not include those working for military contractors off base. The off-base arrests have included hundreds of illegal immigrants hired to prepare field rations by a Texas company that admitted falsifying their employment records. Off-base arrests have also been made in North Carolina, Mississippi and California.

In North Carolina, the military paid contractors $823 million this year and last to perform work at Fort Bragg, Camp Lejeune and Seymour Johnson. Such outsourcing is likely to increase, said defense analyst Loren Thompson of The Lexington Institute.

Under Defense Secretary Donald Rumsfeld's plans for re-engineering the way the military does business, "many, many more activities will be outsourced to contractors," Thompson said. "There's hundreds of thousands of them. The potential for abuse will be there."

Contractors provide the military with civilian instructors in such areas as marksmanship, information management and medical care.

At Fort Bragg, the three foreign language instructors worked at a school run by the Army Special Operations Command, which oversees such elite units as the Green Berets (search) and the Rangers.

But command spokesman Lt. Col. Hans Bush said that the place where the instructors worked is not considered a sensitive location and is used for many unclassified courses.

The instructors worked for Orlando, Fla.-based B.I.B. Consultants (search). Under Pentagon policy, it is the responsibility of the contractor to verify that an employee is legally able to work in the United States, and B.I.B said its background checks of the three instructors came back clean.

Such background checks usually consist of asking for a driver's license and a Social Security card.

Security is under review at Fort Bragg, a base that was once an open post where anyone could drive unescorted, even to the commanding general's front door. Under the Pentagon's base restructuring plan, Bragg is slated to become home to more command offices and the generals who lead them.

"It's certainly an attractive target," Hayes said.