Moscow, April 28 -- The Soviet Union announced today that there had been an accident at a nuclear power plant in the Ukraine and that "aid is being given to those affected."
The severity of the accident, which spread discernable radioactive material over Scandinavia, was not immediately clear. But the terse statement, distributed by the Tass press agency and read on the evening television news, suggested a major accident.
The phrasing also suggested that the problem had not been brought under full control at the nuclear plant, which the Soviet announcement identified as the Chernobyl station. It is situated at the new town of Pripyat, near Chernobyl and 60 miles north of Kiev.
The announcement, the first official disclosure of a nuclear accident ever by the Soviet Union, came hours after Sweden, Finland and Denmark reported abnormally high radioactivity levels in their skies. The readings initially led those countries to think radioactive material had been leaking from one of their own reactors.
The Soviet announcement, made on behalf of the Council of Ministers, after Sweden had demanded information, said in its entirety:
"An accident has occurred at the Chernobyl nuclear power plant as one of the reactors was damaged. Measures are being taken to eliminate the consequences of the accident. Aid is being given to those affected. A Government commission has been set up."
The mention of a commission of inquiry reinforced indications that the accident was a serious one. [United States experts said the accident probably posed no danger outside the Soviet Union. But in the absence of detailed information, they said it would be difficult to determine the gravity, and they said environmental damage might conceivably be disastrous. Page A10. [The Chernobyl plant, with four 1,000-megawatt reactors in operation, is one of the largest and oldest of the 15 or so Soviet civilian nuclear stations. Nuclear power has been a matter of high priority in the Soviet Union, and capacity has been going into service as fast as reactors can be built. Page A10.] Pripyat, where the Chernobyl plant is situated, is a settlement of 25,000 to 30,000 people that was built in the 1970's along with the station. It is home to construction workers, service personnel and their families.
A British reporter returning from Kiev reported seeing no activity in the Ukrainian capital that would suggest any alarm. No other information was immediately available from the area.
But reports from across Scandinavia, areas more than 800 miles to the north, spoke of increases in radioactivity over the last 24 hours.
Scandinavian authorities said the radioactivity levels did not pose any danger, and it appeared that only tiny amounts of radioactive material had drifted over Scandinavia. All of it was believed to be in the form of two relatively innocuous gases, xenon and krypton. Scandinavian officials said the evidence pointed to an accident in the Ukraine.
In Sweden, an official at the Institute for Protection Against Radiation said gamma radiation levels were 30 to 40 percent higher than normal. He said that the levels had been abnormally high for 24 hours and that the release seemed to be continuing.
In Finland, officials were reported to have said readings in the central and northern areas showed levels six times higher than normal. The Norwegian radio quoted pollution control officials as having said that radioactivity in the Oslo area was 50 percent higher.
Since morning, Swedish officials had focused on the Soviet Union as the probable source of the radioactive material, but Swedish Embassy officials here said the Soviet authorities had denied knowledge of any problem until the Government announcement was read on television at 9 P.M.
The first alarm was raised in Sweden when workers arriving at the Forsmark nuclear power station, 60 miles north of Stockholm, set off warnings during a routine radioactivity check. The plant was evacuated, Swedish officials said. When other nuclear power plants reported similar happenings, the authorities turned their attention to the Soviet Union, from which the winds were coming.
A Swedish diplomat here said he had telephoned three Soviet Government agencies - the State Committee for Utilization of Atomic Energy, the Ministry of Electric Power and the three-year-old State Committee for Safety in the Atomic Power Industry -asking them to explain the high readings over Scandinavia. All said they had no explanation, the diplomat said.
Before the Soviet acknowledgment, the Swedish Minister of Energy, Birgitta Dahl, said that whoever was responsible for the spread of radioactive material was not observing international agreements requiring warnings and exchanges of information about accidents.
Tass, the Soviet Government press agency, said the Chernobyl accident was the first ever in a Soviet nuclear power plant.
It was the first ever acknowledged by the Russians, but Western experts have reported at least two previous mishaps. In 1957, a nuclear waste dump believed related to weapons production was reported to have resulted in a chemical reaction in the Kasli areas of the Urals, causing damage to the environment and possibly fatalities. In 1974, a steam line exploded in the Shevchenko nuclear breeder plant in Kazakhstan, but no radioactive material is believed to have been released in that accident.
Soviet authorities, in giving the development of nuclear electricity generation a high priority, have said that nuclear power is safe. In the absence of citizens' opposition to nuclear power, there has been virtually no questioning of the program.
The terse Soviet announcement of the Chernobyl accident was followed by a Tass dispatch noting that there had been many mishaps in the United States, ranging from Three Mile Island outside Harrisburg, Pa., to the Ginna plant near Rochester. Tass said an American antinuclear group registered 2,300 accidents, breakdowns and other faults in 1979.
The practice of focusing on disasters elsewhere when one occurs in the Soviet Union is so common that after watching a report on Soviet television about a catastrophe abroad, Russians often call Western friends to find out whether something has happened in the Soviet Union.
Construction of the Chernobyl plant began in the early 1970's and the first reactor was commissioned in 1977. Work has been lagging behind plans. In April 1983, the Ukrainian Central Committee chastised the Chernobyl plant, along with the Rovno nuclear power station at Kuznetsovsk, for "inferior quality of construction and installation work and low operating levels."
-- U.S. Offers to Help AGANA, Guam, Tuesday, April 29 - Donald T. Regan, the White House chief of staff, said today that the United States was willing to provide medical and scientific assistance to the Soviet Union in connection with the nuclear accident but so far there had been no such request.