TOKYO, JULY 9 (SATURDAY) -- North Korean radio reported today that the nation's self-styled "Great Leader," Kim Il Sung, had died Friday of an apparent heart attack, placing in doubt the leadership of a Communist state that the Clinton administration has described as a threat to peace.

The 82-year-old dictator was the only ruler North Korea has had, taking command with the blessing of the Soviet Union when the Korean peninsula was split into two nations in 1948. He was revered by his 21 million countrymen.

Kim Il Sung had hoped to achieve what no other Communist ruler ever did -- a monarchial succession, with his son, Kim Jong Il ("The Dear Leader") taking power in his place. But Western analysts have questioned whether the 52-year-old son has the charisma or the backing he would need to gain full control. Radio Pyongyang reported today that Kim Jong Il had been named to head the committee organizing his father's funeral, an appointment that in Communist regimes has often signaled a successor.

The "Dear Leader" is a figure of deep mystery, rarely seen in public and barely mentioned in North Korea broadcasts. He is known to love movies and once kidnapped a pair of South Korean movie producers to help him build his own Pyongyang film studio. He is almost never introduced to foreign visitors, and his only published statements in recent years have been hortatory calls for greater sacrifice from the workers.

North Korea is one of the poorest and most primitive nations in the world. There have been many reports of rural uprisings and attempted coups in recent months as hunger and desperation spread from ordinary people to the military.

But the nation's deep reverence for the "Great Leader" had helped the regime face down all challenges. The key question now is whether the son can hold off the opposition as effectively as his father did.

North Korea has a million-member military equipped with modern weapons. The nation also has some amount of plutonium, the basic fuel of nuclear weapons; CIA analysts have said Pyongyang is determined to arm itself with nuclear weapons, and may already have built a bomb.

Kim's death was announced hours after his government opened talks with the United States in Geneva about North Korea's nuclear program. Washington hoped to obtain North Korea's agreement to stop further processing of nuclear materials capable of being used in nuclear weapons in exchange for new aid programs. {Related story, Page A13.}

President Clinton expressed his hope that the talks "will continue as appropriate." In a statement issued this morning at the Group of Seven economic summit in Naples, Clinton said: "I extend sincere condolences to the people of North Korea on the death of President Kim Il Sung. We appreciate his leadership in resuming the talks between our governments."

Kim had looked healthy and vigorous in public appearances recently. He told former president Jimmy Carter just two weeks ago that he planned to rule for 10 more years. During that time, he had reportedly hoped to cement his son's position as his successor.

But Radio Pyongyang announced that he had suffered a sudden heart ailment Thursday and died at 2 a.m. Friday.

The reports prompted immediate speculation among Pyongyang-watchers that there could have been foul play. In the past month, Kim Il Sung has taken several steps that seemed to be accommodating toward the United States. Some analysts say these moves were strongly opposed by hard-liners within the Pyongyang regime.

In his meeting with Carter last month, Kim Il Sung agreed to a first-ever summit meeting between the leaders of North and South Korea. The session had been scheduled to start July 25.

One early test of how stable things are in Pyongyang will be to see what the government now has to say about that summit session.

If the meeting goes ahead, with Kim Jong Il representing the North, that would be a sign that the "Dear Leader" has successfully inherited his father's mantle. If the North cancels or postpones the summit, that might indicate a power struggle within the regime.

North Korean broadcasts monitored in Tokyo by the Japanese network NHK said that the "Great Leader" would lie in state at his lavish Greco-Roman capital building in Pyongyang until July 16, with funeral ceremonies tentatively planned for the next day. In an announcement characteristic of North Korea's go-it-alone style, the broadcasts said no foreign mourners would be welcome for the funeral.

Immediately after announcing the death of the "Great Leader," Radio Pyongyang began playing songs honoring his son, NHK reported.

The younger Kim had previously been named commander of North Korea's armed forces -- despite the fact that he reportedly refuses to board an airplane. But there are two remaining posts he must assume to assure his rule: head of the government, and leader of the Workers Party, the nation's only legal political party.

There were conflicting reports here today about the younger Kim's status. At one point, NHK said a North Korean broadcast had named the late ruler's son as presiding officer of the civil government, but later reports indicated that succession was still unclear.

The people of the Korean peninsula have shared a common language and culture for thousands of years. But the nation was split between the Communist North and the pro-Western South just after World War II, and remains the world's last bastion of Cold War hostilities.

In the past two decades, however, capitalist South Korea has leaped a vast distance beyond the impoverished North in terms of wealth and standard of living. North Korea has tried to ban contacts with the outside world -- no mail, no telephone connections and no broadcasts from other countries are permitted -- to keep its people ignorant of the South's progress.

But travelers to North Korea and a small stream of refugees say people there have become increasingly bitter about the Kim regime -- and increasingly aware of better conditions in the South. With the beloved leader dead, it is possible that North Koreans will try to flee the country in large numbers.

Another threat could be a military coup against the "Dear Leader" and the ruling clique. Just this spring, according to recent defectors to South Korea, about 10 top officers of the army attempted a coup, but it was put down by officers loyal to Kim Il Sung. According to the defectors, Kim then had the coup leaders burned at the stake, with their families watching.

The details of Kim Il Sung's life are shrouded in mystery, because his government created a vast library of myth about him to justify his self-declared stature as "father of his country."

But he was evidently born in Korea in 1912, just after the Japanese had conquered and colonized the peninsula. His father, an early communist, was a resistance fighter against the Japanese. But he left Korea for China when Kim Il Sung was 13 years old.

Kim Il Sung was trained by Chinese and Soviet Communists, and came to know Joseph Stalin in Moscow near the end of World War II. When the Korean Peninsula was divided, Stalin sent Kim back to North Korea, and created the myth that Kim Il Sung was the main who defeated Japan and liberated Korea. That tale was the source of Kim's personal power for the next 46 years.

The "Great Leader" launched the Korean War with an invasion of the South in 1950. After the North's failure in that war, he subsequently used guerrilla raids, sabotage and terrorist attacks against the South.

But in the last month before his death, he dropped most of his militaristic rhetoric and insisted he wanted to co-exist peacefully with South Korea. His agreement to the summit meeting scheduled for two weeks from now was seen as a major breakthrough toward better North-South relations.

News services reported:

Residents of North Korea's capital wept hysterically after hearing the news of their president's death, a Beijing-based reporter accredited to Pyongyang said Saturday.

Krzysztof Darewicz, a correspondent for the Polish news agency PAP, said he had been in contact with his sources in Pyongyang by telephone.

He said the announcement of Kim Il Sung's death had stunned the capital. "There is mass shock and hysteria," he told news services. "In our embassy the gardeners and translators just sit and cry. People who tried to go shopping said they could not because shop assistants do nothing but cry."