MOSCOW (AP) _ A 23-year-old firefighter who was fatally injured while fighting to control the blaze at the Chernobyl nuclear reactor kept working even after two comrades collapsed with radiation sickness, a Soviet newspaper said today.

The Communist youth newspaper Komsomolskaya Pravda said Viktor Kibenok died of burns and radiation 15 days after the April 26 accident.

It said he was among firefighters initially summoned to the blaze who spent much time on the roof of the building housing the nuclear reactor. The fire ''burned with a crackle, giving off suffocating smoke,'' the paper said.

One by one, Kibenok's colleagues collapsed from radiation sickness, according to the newspaper's account. First, Vladimir Tishchura began writhing. ''Viktor, Volodya feels bad,'' yelled another firefighter, Vasily Ignatenko, referring to Tishchura. The newspaper said, ''After that, Nikolai Vashchuk swayed and fell flat on his back.''

Kibenok ''held up, being on the most dangerous place - above the reactor,'' the newspaper said. ''But what Viktor didn't know then was that further below, there were a few more people who already couldn't stand.''

The account said that Tishchura, Ignatenko, Vashchuk and another firefighter, Vladimir Pravik, all later died of injuries.

Other Soviet newspapers today named three plant workers they said died of injuries received in the accident. Soviet leader Mikhail S. Gorbachev on Wednesday identified two other men who died immeditately after the explosion at the plant.

The official Tass news agency on Thursday said that 10 days after the accident, three plant workers volunteered to dive into a pool of radiation- contaminated water under the damaged reactor to drain the water.

If the white-hot core of the reactor had dropped into the water, Tass said, it could have set off steam explosions that would have spread radioactive contamination even farther.

The three men in wetsuits dove into a pool, probing with underwater searchlights for two small valves that would allow the pool to drain, Tass said.

It quoted one of the men, Alexei Ananenko, as telling Soviet journalists, ''When the searchlight beam fell on a pipe, we were joyous: The pipe led to the valves.

''We heard the rush of water out of the tank. And in a few more minutes we were being embraced by the guys,'' Tass quoted Ananenko as saying.

Ananenko was asked by his boss to go into the contaminated water, but also was told he could refuse the hazardous assignment.

''But how could I do that when I was the only person on the shift who knew where the valves were located?'' Tass quoted him as saying.

The report did not mention if any of the men had suffered ill effects since their dive.