Moscow — Originally hailed as a heroic victory against terrorism, the storming of a Moscow theatre was cast in shadow Sunday as former hostages continued to die from the effects of a mysterious gas used to subdue their captors.

Authorities announced 27 more deaths Sunday, bringing to 117 the number of hostages who died in the rescue effort. Moscow's chief physician said that of Saturday's victims, only one died of a gunshot wound, with the rest succumbing to the effects of the gas. More than 150 hostages remained in critical condition Sunday night.

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The Russians have acknowledged using a gas that they have likened to an anesthetic in the raid, but have refused to specifically identify it. Experts have speculated that the substance may have been a gas form of a powerful sedative such as Valium, or benactyzine, a hallucinogenic drug widely researched in the 1960s. Others guessed that it was a nerve agent left over from Cold War stockpiles.

Anesthetist Yevgeny Yevdokimov told reporters at a news conference Sunday that the mystery substance's fatal effects were exacerbated by the weakened condition of the hostages, who had spent 58 hours in captivity under high stress and with little food or water. The doctors also said they were not told what gas was used, which introduced an element of chaos into the treatment process.

The Russian government has not officially acknowledged that any hostages died from the gas. But President Vladimir Putin went on national television Saturday night to apologize for the high number of deaths.

"I would like to address primarily the relatives and friends of those killed. We could not save everyone," Mr. Putin said in the broadcast, wearing a black suit and black tie. "Please forgive us." The Kremlin announced that Monday is to be a national day of mourning for the victims.

On Sunday, Prime Minister Jean Chrétien and other foreign leaders would not criticize the Russians' use of gas, although a White House spokesman also refused to endorse the move.

"We don't know what all the facts are," Ari Fleischer said.

Most of the 50 militants who held the theatre at gunpoint also died in the raid, and there were reports that many were shot in the head while unconscious. But one special-forces trooper said on Sunday that a number of the hostage-takers remained conscious throughout the rescue operation.

The guerrillas "were fully conscious, and we had to act very precisely, because we had no time," he told reporters, noting that a number of squad troopers were "wounded or stunned," though not killed. It was unclear why the gas would have worked on the hostages but not the hostage-takers.

Police were searching Sunday for militants who might have escaped the incident's bloody climax, and the Interfax news agency reported that a Chechen woman allegedly involved in the hostage-taking was arrested in hospital, trying to pass herself off as a victim.

As the search continued, police remained on alert for a secondary attack. Heightened security at the hospitals meant that many friends and relatives were prevented from visiting those being treated for the effects of the gas. Some were still waiting to find out whether their loved ones had survived the ordeal.

"I am looking for my son — here is his photo. He is called Dmitry Rodionov, he was born in 1984. I cannot find him, he is on none of the lists," a distraught woman in her 40s told reporters.

The leading Ekho Moskvy radio station said former hostages "have virtually found themselves under arrest" as police press them for information about the militants.

Russia's mood ranged from sombre mourning to mounting anger at those who launched the audacious attack.

Whatever the final death toll, the most enduring impact of the hostage-taking may well be a hardening of Russian opinion toward Chechnya. Over the weekend, one of the few allies in the Russian parliament of Chechen leader Aslan Maskhadov publicly denounced him as a "terrorist."

Boris Nemtsov, leader of the liberal Union of Right Forces party in the Duma, said that after the hostage-takers invited him to help negotiate an end to the crisis, he learned that they were getting their orders from Mr. Maskhadov. He called the revelation a personal disappointment.

"Maskhadov now can lose any chance of becoming a partner for negotiations. He is in a terrible situation," Mr. Nemtsov said. "A peace process is needed, but I think that the Russian authorities and the Russian public won't forget the Moscow events and Maskhadov's role in them soon."

Mr. Maskhadov's inner circle tried yesterday to distance the hostage-taking from the Chechen leader, who won a 1997 election in the republic soon after it won de facto independence from Moscow in a bloody civil war that has since resumed.

"We said from the beginning: These are not our methods," said Akhmed Zakayev, an envoy for Mr. Maskhadov.

But the Kremlin said during the weekend that it is planning an aggressive sweep of Chechnya to arrest those suspected of having ties to the hostage-takers.

Mr. Nemtsov warned that such a move will lead to more terrorist attacks, and in a grim warning from beyond the grave, one of the militants killed Saturday echoed that sentiment.

"This is not all," the female guerrilla said in a television interview that aired after the raid was over. "There are many more of us, and this will repeat."