KIEV, UKRAINE -- For the last six years, Anatoly Stepanovich Dyatlov has been haunted by the memory of nuclear catastrophe.

Dyatlov, tall, thin and looking older than his 62 years, was the engineer in charge of reactor No. 4 at the Chernobyl nuclear power plant when it exploded six years ago yesterday. In the eyes of the Soviet justice system, he personally bears much of the responsibility for the world's worst nuclear disaster. Soon after the catastrophe, he was found guilty of criminal negligence and sentenced to 10 years in prison.

According to the official version of events, Dyatlov violated the most elementary safety precautions on the night of April 26, 1986. Anxious to complete a scientific experiment that had been ordered by Moscow, he bullied his subordinates into taking unnecessary risks. His incompetence -- combined with mistakes by other Chernobyl employees -- led directly to the destruction of the reactor and the spewing of radioactive particles across a wide area of Europe.

Seated in the living room of his apartment in Kiev, 18 months after his early release from prison as part of a general amnesty for Chernobyl officials, Dyatlov tells a quite different story from the official version. He said he and other Chernobyl operators were made scapegoats for the designers of a dangerously unstable reactor. In his view, blame for the disaster rests entirely with the leaders of the Soviet scientific establishment and their political patrons.

"I found myself confronted with a lie, a huge lie that was repeated over and over again by the leaders of our state and simple technicians alike. These shameless lies shattered me," said Dyatlov. "I don't have the slightest doubt that the designers of the reactor figured out the real cause of the accident right away but then did everything to push the guilt onto the operators."

The details of that night -- especially the moments before and after the first explosion at 1:24 a.m. -- are ingrained in Dyatlov's mind. He drew a diagram showing who was standing where in the control room when a sudden power surge caused a huge increase in steam pressure in the reactor, leading to a series of explosions.

Of the dozen or so people in the control room, five died agonizing deaths from radiation burns in the days immediately after the disaster. Dyatlov himself received a potentially fatal dose of radiation and is now a permanent invalid, finding it difficult to walk more than a few steps without exhausting himself.

Measured by the amount of contamination it produced, the Chernobyl explosion was equivalent to more than 10 of the atomic bombs dropped on Hiroshima. According to the Ukrainian health ministry, 6,000 to 8,000 people have already died as a result of being exposed to heightened radiation. Hundreds of thousands of people living in northern Ukraine and southern Belarus have been evacuated from their homes.

As he told his story, the former deputy chief engineer of the Chernobyl plant smoked one cigarette after another, as if oblivious to further health hazards. At the same time, however, Dyatlov obsessively picked pieces of dust off the table, a habit acquired by many Chernobyl evacuees struggling against the presence of decaying radioactive isotopes. He paused frequently to cough or collect his thoughts.

"If I had known then what I know now about what kind of monster this reactor was, I would never have gone to work at Chernobyl. And not only me. Nobody would have worked there," he said.

The immediate chain of events that led to the Chernobyl explosion began with a routine experiment. Dyatlov and his superiors wanted to see whether the reactor could operate under electricity generated by its own turbines. The purpose of the experiment was to produce a backup source of electricity to keep the reactor going in the event of a general power failure.

Several safety features that could have interfered with the test -- including the emergency water cooling system -- were deliberately switched off. Soviet nuclear safety officials accused Dyatlov and other operators of failing to take a number of other precautions that would have prevented the fatal power surge.

To this day, Dyatlov insists that he did everything right. Flatly contradicting the official account, he says that the atmosphere in the control room was completely normal right up until the destruction of the reactor. No one felt the slightest sense of impending danger. The explosion occurred as the reactor was in the process of being closed down following completion of the experiment.

Dyatlov's first thought was that a gas tank must have exploded on the roof. The blast destroyed the ceiling of the control room, bringing piles of plaster down onto the machines below. Instrument panels flickered wildly. "Everyone to the reserve switchboard," screamed Dyatlov, referring to a second control room just down the corridor for use in an emergency.

Seconds later, he countermanded his own order. Computer readouts showed that the turbine pressure was zero, meaning that steam from the reactor was no longer turning the turbines. Pressure in the water channels was also zero, meaning that cool water was no longer being pumped through the reactor. Most alarming of all, the panel showed that the power in the reactor was increasing wildly when it should have been decreasing.

"I thought my eyes were coming out of my sockets. There was no way to explain it," recalled Dyatlov. "It was clear that this was not a normal accident, but something much more terrible. It was a catastrophe."

In Chernobyl-type reactors, the nuclear reaction is controlled by the lowering of dozens of neutron-absorbing rods into the reactor core. Unfortunately, the rods were designed in such a way that the absorbent part is in the middle. When the tip of the rods entered the core, they displaced water, producing a small but significant surge of power. Combined with a number of other circumstances, this surge of power was sufficient to trigger the explosion.

Exactly what happened in the Chernobyl control room may never be known. Several of the key actors, including the shift foreman, died shortly afterwards. Other people in the room were absorbed in their own tasks. Dyatlov may or may not be telling the entire truth about events leading up to the explosion. But it seems clear that neither he nor anyone else considered the possibility that a device that was meant to close down the reactor would have the opposite effect.

It has since been established that the reactor exploded before the control rods could fully descend into the core. But the operators did not know that at the time. Their first reaction was to try to lower them by gravity. Nothing happened. Dyatlov then ordered two young trainees to the reactor hall to pull the rods down manually. It was a decision he now bitterly regrets.

"When they ran out into the corridor, I realized it was a stupid thing to do. If the rods had not come down by electricity or gravity, there would be no way of getting them down manually. I rushed after them, but they had disappeared," he said.

The two trainees, Viktor Proskuryakov and Aleksandr Kudyavtsev, both received lethal doses of radiation and died agonizing deaths. When they reached the devastated reactor, wearing no protective clothing, they found no trace of the control rods. By the time they returned, their entire bodies were covered with a brown nuclear tan.

Dyatlov, meanwhile, decided to inspect the turbine hall below the other side of the control room. He was greeted by a scene of unimaginable devastation. Flames were leaping up through huge holes in the ceiling. Water was spurting in different directions, spilling over the machinery. There was a constant clicking sound from short circuits. Great chunks of roofing had fallen onto the floor, puncturing oil tubes that immediately exploded into flames.

From above, Dyatlov could see people rushing around helplessly with fire extinguishers. Professional firefighters were later summoned from the nearby towns of Pripyat and Chernobyl, and even Kiev. Showing tremendous heroism, they managed to get the fire under control by dawn, but at terrible cost. That first night, 27 firemen were hospitalized with horrifying burns.

The air was thick with radioactive dust, which created a burning sensation in the chest and lungs and a tightening of the skin. The figures on the radiation measurement instruments flickered off the scale. More powerful instruments were locked up in the safe, on the assumption that they would never be needed. Protective clothing was nowhere to be found.

Realizing there was nothing to do in the control room, Dyatlov took a walk around the damaged reactor. He recalled coming across Anatoly Kurguz, a worker from the reactor hall, whose face was covered with blisters hanging down like pieces of dead flesh. Two entire walls of the reactor hall were missing. It was during this walk that Dyatlov received the greater part of his own potentially lethal dose of 550 rad.

By 4 a.m., Dyatlov had had enough. He grabbed three computer printouts from the control room and took them to Viktor Bryukhanov, the director of the Chernobyl plant. Bryukhanov later reported to Moscow that the reactor was still intact, a myth that persisted for many hours and caused a fatal delay in the evacuation of the plant and the surrounding area.

"I don't know how he reached that conclusion. He did not ask me if the reactor was destroyed -- and I felt too nauseated to say anything. There was nothing left of my insides by that time," said Dyatlov.

Unlike the operators of the Chernobyl plant, six of whom were sent to prison for their part in the disaster, the designers of the reactor were never punished. The principal designer, Anatoly Aleksandrov, a past president of the Soviet Academy of Sciences, still refuses to concede that there was anything wrong with his reactor.

Communist Party leaders who covered up the scale of the disaster and lied about the number of casualties also have escaped punishment. A week after the catastrophe, Kiev residents were ordered to attend a May Day parade in the center of the city to show the world that everything was normal, even though the wind was blowing directly from Chernobyl.

Documents published last week by the now independent newspaper Izvestia show that party leaders from Mikhail Gorbachev down concealed the danger to the civilian population from Chernobyl. Soviet leaders effectively denied medical care to tens of thousands of people living in contaminated areas by secretly decreeing a 10-fold increase in the amount of radiation considered safe. They also permitted meat and milk from the contaminated area to be mixed with produce from other regions.

"What happened after Chernobyl was what always happens in these cases. The investigation was carried out by the very people who were responsible for the faulty design of the reactor," said Dyatlov. "If they had admitted that the reactor had been the cause of the accident, then the West would have demanded the closing down of all other reactors of the same type. That would have dealt a blow to the whole of Soviet industry."

Western experts were at first inclined to accept the Soviet explanation that operator error was chiefly responsible for the Chernobyl disaster. But a recent report by the International Atomic Energy Agency Agency in Vienna pinned most of the blame on a series of fundamental flaws in reactor design.

Since the Chernobyl disaster, some of these flaws have been corrected. The design of the control rods has been improved so that they can no longer cause a sudden power surge as they did at Chernobyl. But dozens of other problems remain, and the 15 other Chernobyl-type reactors still fall far short of Western safety standards.

Last month, a Chernobyl-type reactor near St. Petersburg was temporarily shut down following a leak of radiactive gases. A sticky valve shut off cooling water in one of 1,661 pressurized fuel tubes that run through the graphite core of the reactor. Dyatlov fears that a multiple tube failure could lead to a disaster on a similar scale to Chernobyl.

"The statistics show that a multiple tube failure is highly improbable. But the people who are telling us this are the same people who lied about Chernobyl. So why should we believe them?" he asked.