Congress is moving to close a loophole in the law that has left private security contractors in Iraq like Blackwater immune to criminal prosecution, despite warnings by the White House that expanding the law could cause new problems.

The House was expected to pass legislation on Wednesday by Rep. David Price, D-N.C., that would extend criminal jurisdiction of U.S. courts to any federal contractor working alongside military operations. Senate Democratic leaders said they planned to follow suit as soon as possible and send the measure to President Bush to sign.

The legislation comes amid a string of allegations involving Blackwater USA employees hired by the State Department to protect diplomatic personnel in Iraq. In one case, a drunk Blackwater employee left a Christmas eve party in Baghdad and fatally shot the guard of one of Iraq's vice presidents. The contractor was fired, fined and returned home to the United States, but no charges have been filed.

More recently, Blackwater guards were involved in a Sept. 16 shootout that left 11 Iraqis dead. The FBI is currently investigating the incident.

But whether charges can be brought against any of the contractors is unclear, with federal officials citing murky laws governing the conduct of U.S. personnel abroad not hired directly by the military. The current law, called the Military Extraterritorial Jurisdiction Act, covers personnel supporting the mission of Defense Department operations overseas.

Because Blackwater's primary mission is to protect State Department officials, defense lawyers would likely argue successfully that the law doesn't apply.

At the same time, U.S. contractors are immune from prosecution by Iraqi courts.

White House officials say they support increasing accountability of contractors abroad, but worry that the House bill is too vague and may go too far. An administration statement issued Wednesday said the bill would have "unintended and intolerable consequences for crucial and necessary national security activities and operations." The statement did not explain further or give examples.

The White House also cited concerns with stretching FBI resources by mandating they conduct activities overseas. It also is worried that the military can be overtaxed if required to support criminal investigations led by the Justice Department.

Blackwater founder Erik Prince told a House panel Tuesday that he supports expanding the law.

"Beyond firing him for breaking the rules, withholding any funds we can, we can't flog him," Prince said of the intoxicated Blackwater guard. "We can't incarcerate him. We can't do anything beyond that."