In a report Tuesday on cleanup costs of the Chernobyl nuclear accident, the damaged reactor's capacity should have been given as 1,000 megawatts, and its loss represents 0.4 percent of total Soviet electrical production. Also, of the $1 billion estimated cost for the cleanup of the 1979 accident at Three Mile Island, less than $200 million is being paid by the U.S. government.

The Kremlin faces a steep cleanup bill in the aftermath of the Chernobyl nuclear accident, according to western experts here, but the long-range expense depends on what is now a big unknown: how seriously Moscow will pursue the cleanup effort over time.

The lack of official Soviet cost estimates and uncertainty about the standards Moscow will use to monitor the radiation danger have led to wide variations in western projections of the financial losses and cleanup costs. They range upward from $2 billion.

The Kremlin clearly faces a bigger bill for Chernobyl -- which has caused 19 deaths, the evacuation of 92,000 people and radiation fallout over a large area -- than the $1 billion spent by the U.S. government after the 1979 Three Mile Island accident, according to the western experts.

But the costs in lost electric power and decrease of export potential will be minimal, the experts predicted.

What threatens to escalate the Chernobyl cleanup costs is the need for high-priced decontamination technology and manpower, major resettlement programs, and radiation control -- including extensive tests of potential victims and possibly of damaged crops. These activities may go on for years.

Recent Soviet assertions that the West has exaggerated radiation hazards in the aftermath of the Chernobyl reactor accident have led to fears among Moscow-based western officials that long-term decontamination efforts will be subject to cost evaluations in the Kremlin.

Such fears have been fed by these recent contradictions between the Soviet and western evaluations of current health risks:

*A Soviet official responded to the American Embassy warning this weekend that pregnant mothers and children should not drink local milk with assurances that milk sold in Moscow is safe.

*American bone marrow specialist Robert Gale, on his return to Moscow yesterday to continue treatment of Chernobyl victims, stressed the dangers facing the "50,000 to 100,000" potential radiation victims over many years. The Soviet press has not mentioned the potential victims at all. Today, the Communist Party newspaper Pravda, quoting an unnamed "atomic expert," said that those who have fled the disaster area should "come back home and start working normally."

*Soviet officials, balking at the European Community's ban on food from the affected region, dismissed the move as political and not rooted in real health risks.

*Western countries are warning against travel to the area surrounding Chernobyl. Pravda, on the other hand, indicated that two reactors at the accident site will start up by the end of this year.

Ukrainian Prime Minister Alexander Lysanko told diplomats last week that the accident caused "considerable" financial loss, the government newspaper Izvestia reported. "We have not yet assessed them," he added.

Indications are that current Soviet decontamination efforts do not spare expenses. A team of senior Soviet scientists and officials is apparently deployed at Chernobyl full time. In an article last week about the evacuees, Pravda said more than 10,000 new houses would be built in the region to which some of the 92,000 evacuees have been moved. Evacuees have been given $250 stipends, Pravda said.

Robot cars have been imported from West Germany to allow probes into the contaminated area from a distance. Other sophisticated equipment has been brought in from other countries, including France, to buttress Soviet technology. Aside from military hardware, one western analyst said, "this is the most expensive machinery available on the western market."

The shutdown of the damaged reactor at block No. 4, whose estimated price was $1.25 billion, has caused the single biggest financial loss.

Cleaning out the reactor core will also require an unprecedented joint effort using Soviet and western technology, according to outsiders' estimates.

If Moscow succeeds in plans for an early start-up of the three other Chernobyl reactors, the loss of the 28,000-megawatt reactor in Block No. 4 will result in a decrease of 4 percent of the Soviet electrical output, according to a Moscow-based energy analyst.

Compensation for the loss will likely come in heavier use of other energy sources such as oil, or more reliance on other Ukrainian-based nuclear reactors.

In the coming summer months, when energy use is light, the strains of power shortages are unlikely to show. "But some Ukrainians may be without electricity this winter," a western analyst said.

Despite frantic grain market gyrations following the Chernobyl incident, western agricultural experts here consider the potential threat to Soviet agricultural earnings minimal.

In the end, the Soviet Union may recoup whatever food losses it suffers by increasing agricultural imports from the East Bloc, one western analyst said.

The incident could result in a net food gain for the Soviet Union, but a net loss for its East Bloc allies, according to the analyst. Following the EC ban on the import of food from the East Bloc, communist countries like Hungary could be left holding agricultural surpluses.

Work brigades throughout the Soviet Union have been called upon to contribute a day's salary to the Chernobyl rescue work. A work force of 130 million giving an average of $12.50 each could defray a considerable part of the Chernobyl expenses.

In Moscow, a concert will be held Friday to benefit the Chernobyl victims, Soviet sources said.