Russia moved aggressively today to deflect criticism of its handling of last week's hostage crisis and implicate the leadership of the Chechen separatist movement in the seizure of a crowded theater in central Moscow.

Displaying defused explosives and playing recordings of intercepted telephone conversations, Russian officials tried to remind the world of the threat posed by the Chechen guerrillas, who took more than 800 people hostage. They also sought to link the guerrillas to Aslan Maskhadov, the Chechen president turned rebel leader.

Phone calls between hostage-takers inside the theater and compatriots in Chechnya and elsewhere during the siege "clearly indicate that Mr. Maskhadov was fully informed about what was happening," said Sergei Yastrzhembsky, a special assistant on Chechnya to Russian President Vladimir Putin. "And the people who were in the concert hall also acted with him being aware of what they were doing."

As a result, Yastrzhembsky ruled out new peace negotiations in the war that has ravaged the breakaway republic in southern Russia for the past three years, on top of an earlier war in 1994-96. "Can you name any leader with whom negotiations could be held meaningfully?" he asked. "I am no stranger to the situation in Chechnya, but I don't know any such people."

The elaborate news conference, held under tight security by Yastrzhembsky and other senior officials, came five days after authorities pumped a derivative of the opiate fentanyl into the theater to subdue the guerrillas. The gas ended up killing 117 of the 119 hostages who died during the crisis, according to medical authorities, and Russia compounded the controversy by refusing for several days to identify the substance, even to the doctors treating the freed captives.

Officials expressed no regrets today about either the gas or the secrecy. Alexander Zdanovich, a spokesman for the Federal Security Service, said the gas was not banned under international treaties and should not have been lethal. "There is a consensus among the experts we consulted that this drug could not have caused death," Zdanovich said. Likewise, Moscow Mayor Yuri Luzhkov said all the necessary medical resources were available. "I cannot in any way find fault with the services provided," he said.

As for declining to identify the gas until Western medical experts figured it out on their own, Zdanovich said the priority was "not to damage the security interests of the Russian Federation."

Yet the officials admitted they were puzzled about the effectiveness of the tactic. While the gas immediately rendered many in the theater unconscious, some released hostages have said they noticed a smell or a mist at least a minute or so before passing out, which would have given the guerrillas enough time to detonate their explosives.

The public relations offensive came as Russian security agents continued to pursue Chechens connected to the incident.

Officials said they had arrested a Chechen militant, Sergei Krym-Gerei, with 18 pounds of deadly mercury that could be used in a terrorist attack. Investigators in Chechnya said they had determined that weapons and explosives were smuggled to Moscow on a shuttle bus from Grozny, the Chechen capital, by wrapping them in plastic and pouring vinegar over the packages to deceive police dogs. A firearms dealer, Akhyad Ichiyev, was arrested on allegations of providing the weapons. And Russian forces surrounded Chechen refugee camps in Ingushetia, the Russian republic adjacent to Chechnya, in a search for other suspects, according to reports from the region.

Moscow also exerted pressure on other countries. One tape played today purportedly captured Movsar Barayev, the leader of the hostage-takers, speaking with an ally in Qatar during the 58-hour siege. Russian officials demanded that Qatar extradite the accomplice, Zelimkhan Yandarbiyev.

It was during that conversation that the involvement of Maskhadov and guerrilla leader Shamil Basayev was discussed. According to the Russian translation of the Chechen-language conversation, the men said the operation was being conducted "with the recognition of Shamil," and that "when the operation was prepared, Aslan and Shamil were present. . . . Shamil was following Aslan's directions."

Maskhadov has denied any involvement in the assault on the theater through a top representative, Akhmed Zakayev. But Zakayev was arrested in Denmark on Wednesday on suspicion of involvement, and Moscow said today it was sending documents to Copenhagen justifying his extradition.

Underscoring the potential danger inside the theater, a Federal Security Service forensics specialist said the guerrillas had set up two large bombs containing 152mm artillery fragmentation explosive charges. He said the rebels also carried 25 explosive belts, 16 hand grenades and 89 homemade grenades -- enough firepower to demolish the building and everyone inside.

In another of the taped conversations, the Chechens reportedly talked about accomplices outside the building, including 100 suicide bombers hiding in Moscow and ready to strike. Yastrzhembsky said that might be just "bluster" because the guerrillas knew their phone calls were being monitored, but he said authorities were searching for the accomplices.

During a video presentation, Vladimir Yeryomin of Russia's Federal Security Service displays one of the explosives recovered at the theater where Chechen rebels held hundreds of hostages.