SEOUL, South Korea — American and South Korean intelligence reports that the North Korean leader, Kim Jong-il, suffered a stroke raise questions that the North’s neighbors have long feared asking. If Mr. Kim dies or is incapacitated, who is going to take over the world’s most isolated and unpredictable regime, now armed with nuclear weapons? And what will happen to a nation-church that has worshiped its “Dear Leader” as a god-like figure?

Mr. Kim suffered a stroke in mid-August but has recovered enough to talk and walk, South Korean lawmakers told reporters after receiving a briefing by the National Intelligence Service.

But Kim Sung-ho, the South Korean spy chief, told the National Assembly’s Intelligence Committee that this was not the first time Mr. Kim had had an operation for a circulatory problem, though nothing else was known about past medical operations, the lawmakers said. There was no sign of unrest in the North, they were told.

“We have intelligence reports that after intensive treatments, his condition has considerably improved,” a spokeswoman of the spy agency said, without confirming the lawmakers’ comments.

There was “no problem” with Mr. Kim, Japan’s Kyodo news agency quoted North Korea’s No. 2 leader, Kim Yong-nam, as saying in Pyongyang, the North’s capital.

“We see such reports as not only worthless, but rather as a conspiracy plot,” another senior North Korean official, Song Il-ho, told Kyodo.

Mr. Kim, 66, long suspected of suffering chronic illnesses, was conspicuously absent from a parade on Tuesday to mark North Korea’s 60th anniversary. Following his absence, American officials said Tuesday that Mr. Kim was seriously ill and was likely to have suffered a stroke weeks ago.

Although both American and South Korean officials said it did not appear that Mr. Kim’s death was imminent, the episode prompted analysts to contemplate the prospects of a chaotic power struggle in case Mr. Kim does not recover enough to resume his tight grip on power.

Mr. Kim took over after his father, Kim Il-sung, the founder of North Korea, died of heart failure in 1994. Long before that, he had been groomed as a successor and was running important state affairs.

In contrast, none of his three known sons or his daughter have emerged as an obvious candidate to take the dynasty into a third generation. If Mr. Kim had intended to pick one but now finds his time running out, analysts both in and outside the Korean Peninsula said on Wednesday, the most likely situation would be the stakeholders in Pyongyang forming a collective leadership.

“The majority view now is that it will be a collective leadership with some member of the Kim family as a figurehead,” said Andrei Lankov, a North Korea expert at Kookmin University in Seoul. “But situations can easily go in an unpredictable direction. Many top generals and some civilian leaders will probably be overcome by their own power lust, so some serious infighting with unpredictable results is likely, too.”

Peter Hayes, director at the Nautilus Institute, a research institution based in San Francisco, guessed that “a leader from the current political elite with strong ties to the military” would take over.

Such a leader would stress continuity while trying to put a slow modernizing process in place. Mr. Hayes and other analysts believe there would be no change in North Korea’s nuclear strategy. Any leader or leaders would continue to cultivate the powerful national myths that permeate North Korean life and propaganda, based on xenophobic nationalism and the personality cult built around Mr. Kim’s father, the national founder revered among North Koreans, Mr. Hayes said.

A potential power vacuum would set off intense diplomatic maneuvering. Washington, whose priority is to denuclearize the North, would do what it could to block the rise of a hard-line military leader, analysts said. China wants North Korea to continue as a buffer against American and Japanese influence, but it has also played a crucial role as a mediator between North Korea and the West. Chinese leaders were angry that North Korea, which relies on financial help from China, pushed ahead with provocative actions like a nuclear test in October 2006.

South Korea abhors the prospects of a sudden collapse of North Korea. It also fears that unrest might invite the Chinese military into the North.

On Wednesday, President Lee Myung-bak of South Korea called a hurried meeting with senior aides to discuss the latest events in the North.

The inner workings of Mr. Kim’s regime are shrouded in mystery. Even experts who have spent a lifetime watching North Korea from the outside find it hard to predict its workings. They pore over the images of rare public events, like Tuesday’s parade, for clues to who is up and who is down in the power order.

They said that even when Mr. Kim dies, it could take days for the news to trickle out.

Despite endless rumors about challenges to his leadership Mr. Kim has maintained a ruthless grip on power, his control such that even his closest aides do not know what the others are doing, according to South Korean intelligence officials.

If Mr. Kim is incapacitated but alive, the outside world will not see him for a long time, said Leonid A. Petrov, a North Korea expert at Australian National University.

Then “the group of generals will come out and tell us that the Dear Leader has authorized us to do this and that, and then they will run the country on his behalf until he is really dead,” Mr. Petrov said.

Aging and ailing confidants of Mr. Kim like Kim Yong-nam and Jo Myong-rok may step in. But the casting votes in any power coalition might be held by younger technocrats like Ri Yong-chol and Ri Je-gang, who run military and organizational affairs at the ruling Workers’ Party, analysts said. Chang Song-taek, Mr. Kim’s brother-in-law, is also considered a contender for power.

Mr. Kim’s eldest son, Jong-nam, 37, would have been the natural choice in a Confucian society that favors the eldest son as heir.

But he has a handicap: his mother, a divorced actress, never legally married Kim Jong-il. She died in Moscow in 2002.

Kim Jong-nam embarrassed his father in 2001 when he was caught trying to enter Japan on a fake Dominican passport. He has since been sighted a few times by Japanese reporters in Beijing. That has raised speculation that he may be on the run from a half brother, Jong-chol, 27, and, before that, Jong-chol’s mother, Ko Young-hee.

Ms. Ko, a Japan-born prima donna of Pyongyang’s premier song-and-dance troupe, gave Kim Jong-il another son, Jong-un, 25. Ms. Ko raised her status, and the fortune of her sons, by accompanying Mr. Kim on his “guidance tours” of the military, the loyal backbone of his rule.

But she reportedly died in 2004, and neither of her two sons is seen in North Korean media.

“My guess is like this: they will keep the Kim family as a social and political institution like the emperor system in Japan, offering symbolic and moral power for North Koreans, but are likely to establish a collective leadership system in which the military will play a key role,” said Shin Gi-wook, director of the Walter H. Shorenstein Asia-Pacific Research Center at Stanford.

“We may, then, witness some political instability in the North,” Mr. Shin added.