WASHINGTON, Sept. 19 - The shooting incident involving private security guards in Baghdad on Sunday that left at least eight Iraqis dead has revealed large gaps in the laws applying to such armed contractors.

Early in the period when Iraq was still under American administration, the United States government unilaterally exempted its employees and contractors from Iraqi law.

Last year, Congress instructed the Defense Department to draw up rules to bring the tens of thousands of contractors in Iraq under the American laws that apply to the military, but the Pentagon so far has not acted. Thus the thousands of heavily armed private soldiers in Iraq operate with virtual immunity from Iraqi and American law.

There have been numerous cases of killings or injuries of Iraqi civilians by employees of private military contractors, including Blackwater USA, the company involved in the shooting on Sunday.

Last December, a Blackwater gunman was reported, during an argument, to have killed a bodyguard for Vice President Adel Abdul Mahdi.

He was whisked out of the country and has not been charged with any crime, said Peter W. Singer, a Brookings Institution scholar who has written extensively about contractors in Iraq.

On Wednesday, Prime Minister Nuri Kamal al-Maliki of Iraq complained of killings of Iraqis "in cold blood" by American armed contractors. He said Sunday's shooting was the seventh such case involving Blackwater. Iraq's government is threatening to throw Blackwater out of the country, a move that would have a striking impact on American operations inside the country.

Publicly, the Bush administration has not said how it would respond if the Maliki government tries to carry out its threat to evict Blackwater, but administration officials and executives in the security contracting industry both said Wednesday that they believed that the White House and the State Department would seek to block any move by Iraq to force the company out.

The issue is already leading to sharp tensions between the governments, and any effort by the United States to force Iraq to keep Blackwater could make the Maliki government appear to be a weak puppet.

For years, government officials and members of Congress have debated what has become in Iraq the most extensive use of private contractors on the battlefield since Renaissance princes hired private armies to fight their battles. The debate flares up after each lethal episode in Iraq, but there has been no agreement on how to police the private soldiers who roam Iraq in the employ of the United States government.

Sunday's shooting, which Iraqi officials have branded "a crime," has led American authorities to suspend temporarily most uses of private contractors as traveling bodyguards, and it has put the issue of security contractors back on the front burner in Washington.

A Blackwater spokeswoman declined to comment Wednesday, but in an earlier statement, the company said that its employees "responded legally and appropriately to an attack by armed insurgents."

Several members of Congress and nongovernment analysts said that the oversight of thousands of private military personnel was plainly inadequate and were urging passage of new laws governing contractors, particularly those carrying weapons. The laws governing contractors on the battlefield are vague and rarely enforced. Senators John Kerry, Democrat of Massachusetts, and Lindsey Graham, Republican of South Carolina, successfully sponsored an amendment to a Pentagon budget bill last year to bring all military contractors in Iraq under the Uniform Code of Military Justice.

The bill did not include State Department contractors, like the Blackwater gunmen involved in Sunday's shooting, but Senator Graham said Wednesday that he intended to try to extend its reach to all civilian contractors in Iraq and other war zones. While contractors are not subject to the military code, some argue they could be prosecuted for crimes abroad under civilian law, but in the case of Iraq, that has not been tested.

"If we go to war with this number of contractors in the war zone, thousands of them armed, you need application of U.C.M.J. to maintain good order and discipline," said Senator Graham, who serves in the Air Force Reserve Judge Advocate General Corps.

"This is a real gap in discipline," he added. "These people are on a legal island."

In the House, meanwhile, Rep. John P. Murtha, the Pennsylvania Democrat who is chairman of the House Defense Appropriations Subcommittee, is pushing legislation that would require the secretary of defense to set new personnel standards for contractors and to establish clear rules of engagement for security contractors operating in Iraq and Afghanistan. Mr. Murtha's panel noted that "the oversight and administration of contracted security services is woefully inadequate."

Even the trade association representing armed contractors called for new regulations to rein in contractors who abuse Iraqi civilians or violate the terms of their contracts with the United States government. "If you're going to be outsourcing this much of our war-fighting capability, you have to have appropriate oversight," said Doug Brooks, president of the International Peace Operations Association, which represents private military contractors including Blackwater.

Between 20,000 and 30,000 civilians work for the United States in Iraq as private military contractors, part of a civilian work force that equals or exceeds the more than 160,000-person military force there. The State Department employs about 2,500 private military personnel, chiefly to guard American diplomats and sensitive facilities there. The three prime security contractors for the State Department are Blackwater, DynCorp International and Triple Canopy. Many of their workers are former military Special Forces troops such as Navy Seals and members of the Army's elite Delta Force.

Officials with other security companies said Wednesday that Blackwater now was the dominant contractor for State Department diplomatic security in Iraq, making it all but impossible for the State Department to operate without the company, at least in the short term. For the moment, the military will provide any security needed by the State Department in Iraq. But officials at other firms said that the State Department has in recent weeks awarded Blackwater another major contract, for helicopter-related services, a strong signal of the close relationship between the department and Blackwater.

"If all Blackwater personnel had to leave the country, there would be no one to provide security for the diplomatic mission in Baghdad, except the U.S. Army," said an executive at another security firm, who spoke on the condition of anonymity to discuss a competitor. "My guess is that they will try to find a way to work this out. But there is no doubt there is a lot of raw feelings with the Iraqis."

The United States government and the Iraqis on Wednesday formed a joint commission to review the case and propose steps to avoid a repeat. But a State Department official in Washington said Wednesday that it may be difficult to reconstruct the event and assign blame because of the unreliability of witnesses and the difficulty of conducting forensic studies in the midst of a war zone.

Tom Casey, a State Department spokesman, said at a briefing for reporters that he could not say what laws might apply to the Blackwater guards who fired until the facts are established.

"Until we have results of the investigation and know what facts we're dealing with and know whether, in fact, any activities that might have violated laws occurred," Mr. Casey said, "you can't really deal with the question of who would have specific jurisdiction or how you would resolve issues of competing jurisdiction that might be out there."