An American intelligence official, who, like others interviewed for this article, spoke on condition of anonymity because assessments about Mr. Kim’s health are classified, said Tuesday that it did not appear that Mr. Kim’s death was imminent. The official said there were no clear indications the North was stepping up preparations for a transfer of authority. The official would not say whether American intelligence agencies expected Mr. Kim to fully recover.

The topic of Mr. Kim’s health came up in discussions between the chief American negotiator on North Korean nuclear issues, Christopher R. Hill, and Chinese officials during a recent trip by Mr. Hill to China, said a Bush administration official. But despite the closer contacts between China and North Korea, the official said, Mr. Hill did not come away with a clear sense of Mr. Kim’s condition, or what would happen in the event of his death.

Earlier this year, the North had agreed to abandon its nuclear weapons programs in return for economic and political rewards from the United States and its allies, a major diplomatic victory for the Bush administration.

But late last month the North Korean government reversed course. Angry that Washington had not removed it from a terrorism list, it said it had stopped disabling its main nuclear complex.

It is now unclear whether Mr. Kim ordered the reversal or whether other North Korean officials were making decisions while he was incapacitated.

Since the founding of North Korea in 1948 under Soviet guardianship, it has had only two leaders: Kim Il-sung and, after his death in 1994, his son, Kim Jong-il. Unlike his father, Mr. Kim has not publicly groomed any of his three sons to eventually take power, said Nicholas Eberstadt, a North Korea expert at the American Enterprise Institute. There are doubts about the abilities of all three sons, and American officials tend to gravitate toward theories that a military committee might take over the country.