MOSCOW - The Russian navy struggled Monday to rescue more than 100 sailors trapped at the bottom of the Barents Sea in a submarine crippled by a major collision. The chance of a happy ending, the navy chief conceded, was ''not very high.''
The Kursk, one of Russia's biggest nuclear submarines, was apparently involved in a collision before it plunged hundreds of feet to the sea floor near the Arctic Circle on Sunday, naval commander Admiral Vladimir Kuroyedov said. It had been taking part in naval exercises off the country's north coast.
Russian officials said the vessel was carrying no nuclear weapons and its nuclear reactors had been switched off, but the reports of serious damage raised concerns about a possible radioactive leak.
Russian and Western submarines sometimes play cat-and-mouse games in the area and have scraped each other in the past, according to reports. But the Pentagon said Monday no U.S. ship or submarine was involved in the collision.
However, the ITAR-Tass news agency said an initial outside inspection of the Kursk by a deep-water apparatus did not support Kuroyedov's version of a crash. The agency cited an expert involved in the operation as saying the submarine could have been damaged by a blast in its bow which caused the torpedo section to fill with water.
By early Tuesday, about a dozen military ships including a nuclear-powered cruiser were at the site of the accident, Russian reports said. A team of ship designers was rushed to the area to help suggest ways to rescue the crew.
''Despite all the efforts being taken, the probability of a successful outcome from the situation with the Kursk is not very high,'' the navy chief said.
The condition of the crew was unknown and the navy did not release an official count. Russian news reports said it carried 117 to 130 servicemen.
The navy said at first that it was in radio contact with the submarine, but later admitted that there was only ''acoustic contact'' that could be the noise of crewmen pounding on the hull.
Navy officials declined to say how long the Kursk could remain submerged before it ran out of air for the crew. Nuclear submarines depend on their reactors to replenish their air supplies.
The Kursk went down far above the Arctic Circle, but the sea was free of icebergs, said meteorological officials in nearby Norway.
Navy officials declined to say how far down the vessel was trapped, but a Norwegian report said the Kursk was some 450 feet down, a depth at which rescue would be difficult because of the crushing water pressure. Various Russian reports said the submarine was 330 to 510 feet down.
White House spokesman Joe Lockhart said the administration ''made clear to the Russians that any assistance we can offer is available.'' He said there had been no request for assistance.
Late Monday, another Clinton administration official said two U.S. Navy submarines were operating in the area at the time of the accident, and one reported having heard an explosion at the site Saturday. The official, who spoke on condition of anonymity, is familiar with U.S. intelligence reports on the matter.
The official said the explosion occurred on Saturday, possibly conflicting with Russian reports that accident happened on Sunday.
Navy spokesman Igor Dygalo said the Oscar-class submarine was not carrying nuclear weapons. The Kursk is designed to carry 24 nuclear armed cruise missiles designed to knock out large surface vessels such as aircraft carriers.
But some Western military analysts were skeptical.
''Normally, all submarines go to sea equipped for war. I would be surprised if they had gone to sea without something,'' said Paul Beaver, a British analyst.
There was also concern about a possible radiation leak from the vessel's two nuclear reactors.
''The problem with the nuclear propulsion system is that if the submarine has damaged itself while it was running aground, then you've got a reasonable chance that there will be some sort of radioactive leakage,'' said Lionel Trippett of the Campaign for Nuclear Disarmament.
Norway, which has a scientific vessel in the region, detected no sign of a radiation leak, said Norwegian Foreign Ministry spokesman Karsten Klepsvik.
Vladimir Gundarov, a submarine specialist at Red Star, the official daily newspaper of the Russian military, said rescuing people from a submarine is very difficult and there is no set procedure. The Russian navy does not have advanced submarine rescue vessels, according to standard naval reference works.
The crew may be able to use on-board capsules to escape, but in the worst case would have to swim out through the torpedo tubes, which would be very dangerous, he said.
In a 1983 Soviet submarine accident, the crew perished when trying to escape from a depth of 180 feet, according to the Norwegian environmental group Bellona, which closely monitors Russia's northern fleet.
The Kursk, launched in 1995, weighs some 14,000 tons, according to Jane's Fighting Ships, an authoritative guide to warships.
Russian nuclear submarines have been involved in a string of accidents in recent decades. The navy, like the rest of the Russian military, is desperately short of money and performs almost no maintenance on its ships.
In the last major accident involving one of Moscow's nuclear submarines, the Komsomolets sank in April 1989 after catching fire 200 miles north of Norway. Forty-two of the 69 Soviet sailors aboard died in the accident and the wrecked hull with its reactor still lies on the sea bottom.