WASHINGTON — As the Bush administration deals with the fallout from the recent killings of civilians by private security businesses in Iraq, some officials are asking whether the contractors could be considered "unlawful combatants" under international agreements.

The question has been raised as an outgrowth of government reviews of the shootings in part because officials want to determine whether the administration could be accused of treaty violations that could fuel an international outcry.

If use of guards poses a potential violation, U.S. officials may have to order limits on what guards can do in war zones, which could leave more work for the overstretched military.

Even unresolved questions are likely to touch off new criticism of President Bush's conduct of the Iraq war, especially given the broad definition of unlawful combatants he has used in justifying prison policies at Guantanamo Bay, Cuba.

The issues surrounding the private security contractors are being examined by lawyers at the State, Defense and Justice departments, and there are disagreements about their status both between agencies and within the Pentagon itself.

The use of private contractors by the U.S. military and governments around the world began long before the U.S invasions of Afghanistan and Iraq, but it has mushroomed in recent years.

On Sept. 16, a Blackwater USA security team guarding U.S. diplomats was involved in a shooting that killed 17 Iraqis. Blackwater said its personnel were under attack, but Iraqis said the team started the shooting.

Other incidents since have come to light, portraying the private guards as aggressive.

The guards also operate under immunity from Iraqi law, granted in 2004 by U.S. officials, and in a murky status with respect to U.S. laws.

The designation of lawful and unlawful combatants is set out in the Geneva Conventions. Lawful combatants are nonmilitary personnel who must operate under their military's chain of command. Others are allowed to carry weapons in a war zone but cannot use offensive force. Under the international agreements, they are allowed only to defend themselves.

But the amount of force being used in Iraq by security companies such as Blackwater has raised questions.

The United States already has faced international criticism about its interrogation techniques and detention procedures — and charges that they do not adhere to international treaties. It was the government lawyers involved in those matters who first raised questions about the legal status of the private security contractors.

Lawyers at the Justice Department are skeptical that the contractors could be considered unlawful combatants, but some legal experts within the State and Defense departments say the contractors' actions in Iraq could be vulnerable to such claims. If that happens, some experts say the United States would have to pull them out of the war zone.

There is wide agreement among legal experts that private contractors are allowed to use force to defend themselves. But exactly when defensive force becomes offensive force is an ill-defined threshold.

For a guard who is only allowed to use defensive force, killing civilians violates the law of war, said Michael N. Schmitt, a professor of international law at the Naval War College and a former Air Force lawyer.

If the contractors were the aggressors in an incident, they could be deemed to be unlawfully using offensive force, said Scott L. Silliman, a retired Air Force lawyer and now a professor at Duke University. They could claim they were defending themselves only if they had been fired upon.

Some Defense Department lawyers say that interpretation is too restrictive. Like soldiers, the security guards should be able to defend themselves if they detect "hostile intent," said the defense official.

But too often, the guards are being dragged into operations where the line between defensive and offensive force is hard to determine, such as escorting a diplomat through a neighborhood that is part of a war zone, as many frequently do.

Many of the current and former government officials say the administration has an obligation under the Geneva Conventions to clarify the status of the contractors. Some are perplexed that the Bush administration failed to resolve these issues — or at least discuss them more thoroughly — before putting contractors on such a complex battlefield.