WASHINGTON - The United States on Monday said Russia faced "no easy way out" of the theater siege by Chechen rebels that left 117 hostages dead, and said the blame lies with the "terrorists" rather than the Russian government.

A gas used by Russian special forces to end the crisis on Saturday killed 115 of the hostages, and the United States has asked for an explanation of the assault.

Russian officials have refused to identify the gas, even to doctors trying to treat the ill. Representatives for the State Department and Pentagon said they did not know what gas was used.

President Bush blamed the rebels who occupied the theater for three days rather than Russian President Vladimir Putin, White House spokesman Ari Fleischer said aboard Air Force One as Bush flew to New Mexico on a campaigning trip.

"The president feels very strongly that the people to blame here are the terrorists; the people who caused this tragedy to take place are terrorists who took hostages and endangered the lives of others," Fleischer said. "This is a tragedy ... but he understands it is the terrorists with whom the blame lies."

The United States has been waging its own war on terrorism by trying to destroy Osama bin Laden's al Qaeda network, which it blames for last year's Sept. 11 attacks on America that killed about 3,000 people.

U.S. Embassy officials in Moscow, who visited hospitals and other locations, found what they believed to be the body of one U.S. citizen, but they were awaiting final identification.

They also found another American who had been inside the theater and was currently in "stable condition," and a U.S. permanent resident who was "also recuperating from injuries," State Department spokesman Richard Boucher told reporters.

"The Russian government was faced with a difficult dilemma as a result of this cruel terrorist act. There was no easy way out of this situation, in which armed terrorists were threatening the lives of so many people," he said.

Boucher said the U.S. view on resolving the Chechen conflict remained that a "political settlement" was required.

"There's no military solution in Chechnya for either side and there's certainly no solution from terrorism," he said.

Boucher said the United States did not know in advance that the Russians were going to use gas in the rescue effort of about 750 people held hostage by about 50 Chechen rebels, some with explosives strapped to their bodies.

'THEIR WACO'

"It's their Waco," said Harvey Kushner, a criminal justice expert at Long Island University.

About 80 members of the Branch Davidian cult died in 1993 in Waco, Texas, when their compound burned down. Federal agents had used tanks to poke holes in the buildings to insert tear gas in an attempt to end the 51-day standoff and force the group out in the open.

Kushner said that in both the Moscow and Waco situations, authorities "should have continued to talk and tried to negotiate."

National security experts speculated that the type of gas used was an opiate or some type of general anesthetic.

"For years people dealing with hostage incidents have been seeking the magic substance that would solve their problem - an odorless, non-lethal, instantaneous knockout gas," said Brian Jenkins, a senior terrorism expert at RAND, a U.S. think tank.

But such a substance did not exist because the impact on a person depended on weight, age and physical condition, Jenkins said. "There is no such thing as a standard dose that covers a very diverse population."

Russian authorities had to make the calculation of the number of people whose lives could be saved in making their decision to use the gas when faced with armed attackers who could detonate explosives and cause hundreds of casualties and possibly bring the structure down, Jenkins said.

"Probably, just on the kinds of calculations one would make, going in to some type of assault without the gas would really have been a very high risk," he said.

Kushner said the Russians may have been deliberately harsh in their methods to send a message to the rebels of the consequences for such action.

"In a way it was very heavy-handed that you had innocents dying, but again they're dealing with a very serious terrorist problem," Kushner said. "And so the message went out - we're not going to take anything from you guys."