The Chernobyl nuclear accident resulted from a poorly planned experiment to determine whether the turbine engine at the plant would keep running in case of a reactor shutdown, Soviet Foreign Ministry spokesman Gennady Gerasimov said today.

"The generator was being tested to see what capacity it had to produce kinetic energy for a period of 40 to 45 seconds in case of an accident," Gerasimov said in a press briefing today.

Explaining that the experiment was "of a technical nature," Gerasimov said it had nothing to do with the military.

"The experiments were not carefully prepared," Gerasimov said. "The necessary precautions were not taken."

In a report released Saturday, the ruling Politburo said that the April 26 accident had been caused by "a series of gross breaches," by reactor operators during an experiment.

Today Gerasimov gave the first official description of what kind of experiment had led to the accident, regarded as the worst in the history of nuclear power.

"When you shut a station, the generator is still working," he said. "They were looking at whether it could produce energy for 40 to 45 seconds before switching over to emergency supplies in case of an accident."

The Foreign Ministry spokesman also made the first suggestion that local workers had botched an otherwise routine experiment.

"The point is not that the experiment was conducted," he said, "but that it was conducted without the necessary precautions."

Initially, Soviet officials reported uncertainty over the causes of the explosion, but on May 21 one official said that experiments were being conducted at the time it occurred.

Previous accounts of the accident have said that the explosion occurred after the reactor surged from 6 percent of capacity to 50 percent and the cooling system failed to handle the overload.

Water and graphite combined, producing hydrogen, which exploded.

The complete findings made by the government commission appointed to investigate the disaster will be submitted to the International Atomic Energy Agency in Vienna in September, Gerasimov said.

The report Saturday by the Politburo, released by Tass following a discussion about the incident, seemed to be made up of excerpts from the special commission report, which Gerasimov said today will have "hundreds of pages."

Gerasimov also denied rumors that Boris Shcherbina, deputy chairman of the Supreme Soviet had been fired as head of the commission.

He said that Shcherbina denied as greatly exaggerated "talk in the United States that he was demoted or fired."

Shcherbina remains head of the commission, but the job of supervising work in the field at Chernobyl rotates among different commission members, Gerasimov said.

Nikolai Lukonin was named minister of the atomic power industry, the official news agency Tass announced Monday, after several Moscow-based officials were fired last week in connection with the Chernobyl accident.

The Politburo report released Saturday blasted the Ministry of Power Engineering and Electrification, and the state atomic power safety commission for irresponsibility, and failure to control experiments at Chernobyl.

Western analysts here have interpreted the firings as a Soviet move to clear the decks before the IAEA conference, where Soviet officials are expected to face renewed criticism about Chernobyl.

Even after the personnel shake-up and new explanations about the Chernobyl disaster, questions remain unanswered about the nature of the experiment, how it resulted in the explosion and fire and whether the other Soviet nuclear reactors undergo similar experiments routinely.

Staving off a barrage of such questions, Gerasimov said they would be answered in the commission's report.

Still, Moscow has insisted that the Chernobyl accident will not deter it from a planned increase in nuclear power output during the next five years.