When Mikhail Gorbachev made his first public appearance after the April 26 Chernobyl explosion, nobody knew whether the emergency measures taken to stop radiation emissions and cool the red-hot reactor core would succeed.

Six days after the accident, the Soviet leader emerged atop Lenin's mausoleum on Red Square to observe the traditional May Day parade. His face was hidden beneath a black hat, and his attention was undoubtedly absorbed by the unfolding catastrophe.

With two dead and others dying, radioactivity drifting across Europe and a reactor meltdown still a possibility, the Chernobyl disaster was growing, with no end in sight.

Gorbachev watched three hours of ceremonies in silence, then withdrew into the Kremlin and remained out of public view for two weeks. When he reappeared, on national television, it was to announce that the worst was over and to sound a battle cry: "The top priority task is to eliminate the consequences of the accident."

Six months later, Gorbachev's exhortation has started to yield results. The Soviet Union has cleared some important hurdles in the struggle to overcome the national tragedy, reviving energy production at Chernobyl and pushing ahead with economic reforms.

Anxious to accelerate recovery from the disaster, the Soviet Union has already resumed operations at one of the three undamaged Chernobyl reactors, with a second scheduled to start up before the end of the year, and has made clear its intentions to pursue its original plans for a major expansion in nuclear power production.

Even the initial threat to the new Soviet leadership's party power base has diminished. Top Soviet nuclear power officials have been fired and 27 Communist Party members expelled to satisfy public outrage over the incompetence that caused the disaster at reactor No. 4.

Many of the country's foremost scientists and politicians have become involved in efforts to restore public confidence. In the past six months, four members of the ruling Politburo have made five publicized visits to the disaster site.

Trust in Soviets Eroded

And yet, the most troubling aspects of the accident -- sloppy experimentation at the plant, failure to alert foreign countries to the radiation cloud, evacuation delays of more than a week and other early blunders -- continue to erode trust in Soviet authorities. Bitterness is still evident among some groups of disaffected Soviets and those directly exposed to radiation dangers, particularly in and near the Ukrainian capital of Kiev.

According to western analysts, the cumulative effect of radiation fallout after six months has wrought extensive ecological damage fanning out from Chernobyl toward eastern and Western Europe and Scandinavia, as well as the Soviet Ukraine and Moldavia.

The Soviets estimate that in addition to the 31 who died from the direct effects of fire and radiation at Chernobyl, another 6,000 deaths from cancer over and above expected levels will occur in the next 70 years. Some western specialists place that figure as high as 24,000. These analysts also dismiss official Soviet estimates that cleanup and relocation costs will total $ 2.98 billion, saying that a sum twice that amount is more likely.

For Moscow, the resumption of energy production earlier this month at one of the undamaged Chernobyl reactors, made possible by entombing the stricken No. 4 reactor in cement and thus cutting off the flow of radiation, was the first milestone in the resolution of the crisis.

Last August, Moscow defused some criticism abroad by admitting that reactor design flaws as well as human error contributed to the disaster. The disarming, and surprising, candor was evident in a 382-page account made available to industry specialists gathered at a special conference of the International Atomic Energy Agency (IAEA) in Vienna.

The Soviets also have begun to assume a more active role in international nuclear safety. They were leading supporters last month of an international agreement requiring countries to report immediately on any nuclear accident that could involve radiation crossing borders. The pact was approved at a special IAEA session, where the Soviet delegation talked of establishing global guidelines for nuclear reactor safety.

Soviet energy officials also managed to get back on track Moscow's five-year plan to more than double its nuclear capacity by making two pledges: safety features would be upgraded at all Chernobyl-type reactors, and Soviet nuclear workers would be retrained to cope with emergencies.

The changes include adapting the fuel system to avoid overheating, putting locks on the control rod drive mechanism in the reactor and adding more control rods.

Calling the results of the August IAEA meeting "very promising," Gorbachev told journalists at an Oct. 12 press conference in Iceland, "Now we have an international mechanism to resolve many important questions relating to safety in nuclear reactor engineering."

The initial three-day news blackout, and the resulting uproar in the West, have given way to a flood of official information about Chernobyl and brought a turnabout in Kremlin policy on reporting disasters.

Chernobyl has also given a push to the general Soviet policy of glasnost, or openness, favored by Gorbachev. In the past two months, the Soviet press has nearly drowned out memories of the initial news blackout with a series of candid dispatches about earthquakes, a shipwreck, a hijack attempt and the sinking of a Soviet nuclear submarine.

Gorbachev's Image Intact

Although Gorbachev's 18-day absence from public view drew criticism in Moscow and abroad, in the end it has helped him emerge from the crisis with his reputation hardly ruffled.

By staying out of the fray in the uncertain days at the beginning of the incident, Gorbachev distanced himself from its darkest moments. "In the end, nobody connected the Gorbachev policy with Chernobyl," said Fyodor Burlatsky, a columnist for the Soviet newspaper Literaturnaya Gazeta, in an interview. "The disorder that reigned there set in many years ago."

Still, it was a disorder that the new Soviet leader inherited, his first domestic crisis. Chernobyl would have been a rugged test for any political leader anywhere. It struck with enough power to derail Gorbachev from the course of leadership he had followed for a year before the explosion.

By official Soviet accounts the most costly domestic accident in postwar history, Chernobyl threatened to drain resources and steal the momentum from Gorbachev's 15-year blueprint for economic reform, which emphasized revamping the nuclear and other energy industries.

Perhaps more important in the long term, the Chernobyl incident exposed the Soviet Union's nuclear vulnerabilities at a time when Gorbachev was exhorting the country to enter a new technological era.

From the outside, it now appears that Gorbachev took an early lead role in resolving the crisis and circumvented potential management conflicts by dispatching some of his closest aides to the scene to settle key problems.

In the end, however, the disaster has extracted a heavy price from the Soviet economy and leadership. For the $ 2.98 billion Moscow says it will lose in energy, resettlement and cleanup costs, it could have bought five reactors the size of the $ 597 million damaged Chernobyl plant.

Moscow Escaped Some Costs

Still, the Kremlin has cleared the first stage of the disaster with a far lower cleanup bill than any other major industrial country would have faced under similar circumstances, according to western specialists.

The main reason: Lower environmental and health standards have spared it the liability payments that western governments would have had to pay. Despite an international effort to extract compensation for crop losses wrought by the Chernobyl radiation cloud, the Kremlin has declined to pay the West one kopeck. And after itemized payments for the reactor, new housing, workers' wages and energy and agricultural losses, there is little money left in the Chernobyl budget for compensating local damage.

The energy shortage resulting from lost power at Chernobyl and repair work at the 11 similar plants will amount to 5 percent of the Soviet Union's 1986-87 power supply, according to Soviet energy officials.

The accident has upset Soviet trade relations, at least temporarily. Planned reactor sales to Finland and Yugoslavia have been postponed. Direct electricity supplies from Chernobyl to Hungary and other energy exports to other East European countries have already fallen off, according to East European sources. Moscow has admitted buying food from its allies to compensate for a European Community ban on East Bloc produce and meat in the aftermath of Chernobyl.

Some of the feared economic repercussions have been avoided. The loss of agricultural production in the region around Chernobyl has been minimized, for example, because most radiation fell short of the Ukrainian wheat belt, affecting less fertile marshlands and sandy soil instead.

Moscow eased part of the pinch on its coffers by assigning sanitation duty to Soviet soldiers, whose wage costs are less than the double wages paid to civilian cleanup crews. It also collected $ 700 million in donations from Soviet workers, and others.

Despite Soviet efforts to readjust the distribution of energy before the winter, the Chernobyl crisis has already had a "marked effect" on the country's energy balance, Dmitry Protsenko of the Soviet Power and Electricity Ministry told the official Soviet weekly Nedelya last week. Brownouts, shifts in the industrial load to off-peak hours, and dimmed advertisement lights in Soviet cities are among the measures being initiated to offset the energy losses, he said.

Down the road, the post-Chernobyl energy problem could get worse. Since the disaster, none of the reactors for seven nuclear power stations that had been planned for 1986 has been commissioned. Protsenko admitted that the startup of three new reactors "was put off till late this year." The main problem, according to some Soviet sources, is recruiting labor to work at the new plants. At Chernobyl Unit 1, where energy production has just resumed, workers were placed on a special rotation, alternating two weeks of work with two weeks of leave to minimize radiation exposure.

Soviet officials have recently announced that two additional reactors will resume operation at Chernobyl before the end of the year. But with one reactor permanently out of commission, a power shortage is inevitable. On the last day of September, the Communist Party newspaper Pravda, taking advantage of the jarring effect of the first snowfall across Russia, reminded its readers in a front-page editorial that the Chernobyl crisis called on them to conserve.

Extensive Environmental Damage

The 18-mile zone around the damaged reactor, cordoned off and evacuated several days after the incident, is now a ghost region of deserted houses. It could remain uninhabitable for the next four years, according to the official Soviet report on Chernobyl.

The effects of the accident on animal and plant life seem uneven, due to the haphazard scattering of radiation within and beyond the zone.

But the most severe effects on the local environment are probably yet to come, the report said. It predicted that the radioactive trail from the earliest releases will seep into the grass, trees and soil for another six months. Soviet specialists expect some forests and marshes in the area to retain contamination for another three to four years.

Only after sufficient decontamination of the entire area, the report said, can the population return. Meanwhile, many evacuees have already taken up new homes and jobs elsewhere.

This summer's countermeasures -- washing buildings and streets and scraping away damaged topsoil -- provided little more than temporary relief, according to the report.

Cesium 137 and some of the other contaminants released are likely to be "persistent and high" in local produce "for several years," the report said.

As long as radioactivity lingers in plants and soil, the local water supplies are also in danger of contamination, despite an all-out effort to dam them against seeping radiation from the reactor, according to western specialists.

Future Casualties Uncertain

The death of Chernobyl plant worker K.I. Luzgakova in early August brought the incident's toll to 31 and ended the first wave of casualties, who were mainly victims of heavy doses of radiation, smoke inhalation and burns. Their deaths shifted attention to the additional cancer fatalities that are expected to climb to the thousands and continue at least through the middle of the next century.

Six months after the accident, the world's experts on radiation are locked in dispute about the number of lives that may be affected by Chernobyl over the long term.

The Soviet Union has refrained from projecting possible casualties from the accident. But in its August report to the IAEA, Moscow provided data that revealed that in the western part of the Soviet Union alone, the death toll will rise between 6,000 and 24,000 over the next 70 years, according to western specialists. In Western Europe, they estimated, another 2,000 are in danger.

Short of premature death, the Chernobyl employes and their children and grandchildren face a long list of formidable illnesses, including leukemia, mutation of genes and various types of cancer.

The risk of death or illness depends largely on the amount of exposure to the Cesium 137, Iodine 131 or other radioactive elements emitted from the damaged plant, or the consumption of contaminated milk and food.

The wide range in projected deaths results, in part, from the unique nature of the threat Chernobyl posed to public health. It is the first nuclear accident in history to produce such a constant, steady stream of low-level releases of radiation. The opportunity to determine what levels of radiation bring on sickness or death has made the 135,000 evacuees from Chernobyl -- dozens of whom are still under treatment -- a case study for an international team of health specialists, including many westerners.

But even for the specialists, the care of Chernobyl victims is a matter of trial and error. Already, Soviet specialists have cast doubt on one controversial decision. Thirteen patients were rushed through bone marrow operations in the hectic aftermath of the incident. Because nine of the 13 died, Soviet doctors have concluded that the risky operations were "only moderately effective."

The early failure of Soviet officials to order a mass evacuation of the Chernobyl vicinity increased exposures to radiation and heightened local vulnerability to illness and death.

According to official Soviet reports, the evacuation of 135,000 was stretched out over a week, with decisions depending on shifting winds bearing radioactivity and differing jurisdictions.

The first mass evacuation in Pripyat, the service town for the Chernobyl facility, did not start until 36 hours after the explosion. A few days later, officials in Soviet Byelorussia, whose border is 10 miles from the damaged plant, tested the air and called for additional evacuations, according to Byelorussian press reports. The town of Chernobyl, 13 miles from the plant, was not evacuated until a week after the accident, following a visit of senior Politburo members to the region.

Partly out of ignorance about the effects of radiation, people living near the Chernobyl plant exposed themselves needlessly to potentially dangerous levels of radiation. Firefighters rushed to the scene of the accident without protective clothing; workers from the plant ignored detours to steal a peek at the damaged facility, according to an official Soviet publication.

For thousands of Soviets living in the vicinity of the plant, no restrictions were imposed on food consumption for two weeks after the accident, according to the official Soviet report. Even after controls were placed on local produce, some local residents gulped down milk with up to 100 times the permissible levels of contaminants, the Soviet report presented to the IAEA said. In an interview, a Moscow-based Soviet microbiologist explained why: "Nobody has informed the public as to what the health hazards of radiation are. Even now, a layman can't follow the complicated, diluted things that have been said in the press."

The Damage Abroad

Lacking the shelters that state control has afforded Moscow, unconvinced by the Soviet Union's plans to redress its reactor flaws, the western nuclear industry has recoiled in response to Chernobyl. In Yugoslavia, the Netherlands and Finland, Chernobyl froze plans for new reactors. In Austria, it killed them.

From the United States to Poland, protesters have demanded a halt to nuclear energy production. Antinuclear politicians in West Germany and Britain, riding the crest of the post-Chernobyl wave, have made the abolition of nuclear power an issue in upcoming elections.

In the wake of Chernobyl, a bid to start up the beleaguered nuclear plant at Seabrook, N.H., has been dealt a setback. In apparent reaction to the evacuation foul-ups after the Chernobyl explosion, Massachusetts Gov. Michael S. Dukakis recently refused to submit evacuation plans for six towns in his state that are within 10 miles of Seabrook, saying that the current proposals were inadequate.

Late last month, advocates of nuclear power met at the IAEA in Vienna to plot the industry's post-Chernobyl course. The outlook was grim. Citing increased hostility, skepticism and fear about nuclear power, Hans Blix, the IAEA director, acknowledged in a speech that Chernobyl has filled the antinuclear movement with "new vigor."

But Washington, Paris, Bonn and other governments that rely heavily on nuclear power to alleviate the costs of oil or avoid the environmental damage of coal are determined to keep Chernobyl from becoming a stumbling block. Since Chernobyl, industry specialists have begun discussions about the nuclear reactor of the future, one that would bear a uniform, internationally approved design.

Radiation from Chernobyl has laid waste to reindeer meat in Sweden, milk as far away as the southern part of West Germany and a season of produce in gardens scattered all over Central Europe, according to reports from various European governments and the World Health Organization (WHO).

At first, winds from Chernobyl blew a cloud of radiation over Poland, Finland and Sweden. Two days later, the winds shifted, sending another cloud of Cesium 137, iodine and other radioactive elements out over Poland, Czechoslovakia, West Germany and lands farther to the west. On Wednesday, April 30, five days after the incident, a cloudburst brought down radiation-laden rain over southern West Germany. In a matter of hours, background radiation in the city of Munich rose 13 times, the WHO reported in its study of Chernobyl's effects on foreign countries.

In the aftermath of Chernobyl, 25 of 34 countries reporting to the WHO on the effects of the accident placed restrictions on the consumption of water, milk, meat and vegetables and on outdoor activities. In several European countries, the adverse effects of the accident are still emerging. Sweden, hit earliest and perhaps hardest, has registered some of the most damaging results. In Swedish Lapland, an entire season of reindeer slaughter has been declared unfit for human consumption. Due to the reindeer's retention of Cesium 137 and the pyschological impact on local herders, Swedish officials fear that the costly livestock may be wiped out for the next six years or more.

The agricultural and environmental consequences of Chernobyl have already cost Stockholm $ 40 million in damages. West Germany's Chernobyl bill has been even higher -- $ 100 million and rising. In all, West European governments say that the disaster will cost them a half-billion dollars in spoiled crops and other damages.

Confusing Reaction in Europe

Caught off guard by the explosion, many European governments rushed out with health warnings and restrictions that wound up confusing local populations. While West Germans were immediately told to avoid milk, leafy vegetables and outdoor swimming, citizens in nearby Belgium were given no government advice for two weeks after the incident, according to the WHO report. In the Netherlands, residents were told to throw out all spinach one day and to bring it to markets to sell the next, WHO reported.

In May, the European Community banned food exported from members of the Council for Mutual Economic Assistance, or Comecon, an organization of the Soviet Union and its allies. EC restrictions were extended for five months in late September.

Taking advantage of the confusion, Moscow rejected all claims from western governments for damages, saying the West had brought a pileup of discarded produce on itself by arousing panic. Six months after the incident, relations are still strained between Moscow and some European capitals, whose post-Chernobyl queries and protests went unanswered. West European diplomats were left to get answers about the accident from the summer-long run of articles in the Soviet press.

But for the Eastern Bloc -- Moscow's main customers for reactors and most obedient allies -- the Kremlin ended up listening to gripes with greater sensitivity.

The loudest public complaints came from Poland. Although the Chernobyl plant lies near the Polish border, Warsaw officials found out about the incident as the rest of the world did: from an official Tass dispatch 2 1/2 days after it occurred.

Besides the dose of radiation it received, Hungary had two additional reasons for concern over Chernobyl. As the Eastern Bloc's major food exporter to Western Europe, Hungary stood to lose the most through the EC ban on produce. And as a major electrical importer from the Chernobyl region, it faced the possibility of energy shortages.

Throughout May, as anger rose in the West over Chernobyl, East European officials trumpeted Gorbachev's mid-June visit to Budapest as a forum for a coming to terms over Chernobyl.

After two days of talks on arms control and security issues, the Eastern Bloc leaders held a final session on June 11. Soon after the doors were shut, Janos Kadar, Hungary's leader and the elder statesman of the bloc, raised the issue of Chernobyl.

Soviet and Eastern Bloc officials have declined to discuss what transpired inside. But within days of the meeting, word leaked out that Moscow was paying hard-earned western currency for Hungarian and Polish meat that had been banned by the EC.