Congress wants to update a law that has protected Blackwater USA and other private security contractors in Iraq from criminal prosecution, but the White House has expressed doubts.

The House was expected to pass legislation on Thursday that would extend the criminal jurisdiction of U.S. courts to any federal contractor working alongside military operations.

Senate Democratic leaders planned to follow suit quickly and send the measure to President George W. Bush.

The legislation by Rep. David Price, a North Carolina Democrat, comes amid a string of allegations involving Blackwater 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; no charges have been filed. More recently, Blackwater guards were involved in a Sept. 16 shootout that left 11 Iraqis dead. The FBI is investigating.

It is unclear whether charges can be brought against any of the contractors. Federal officials cite murky laws governing the conduct of U.S. personnel abroad not hired directly by the military. The current law, 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 probably would argue that the current law does not 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. The White House also cited concerns with stretching FBI resources by mandating that the agency conduct investigations overseas.

Also, officials said they feared the military could be overtaxed if required to support criminal investigations led by the Justice Department.