“That’s not what the president is promising or what everybody is hoping for, but it would be really good and they should take it,” said Jeffrey Lewis, a Korea expert at the Middlebury Institute of International Studies. “You’re not getting rid of the weapons, but putting yourself on the path where someday they might not be needed. Maybe not in Kim Jong-un’s lifetime, but it is still worth making that progress, especially because 2017 was really scary.”

Mr. Trump’s desire for a quick, tweetable triumph could leave room for professional diplomats and nuclear experts to hammer out a longer-term agreement with North Korean officials, some analysts say.

“He will come out and say, ‘Where is my peace prize?’ ” said Suzanne DiMaggio, a director and senior fellow at the New America research group who has been involved in unofficial talks with North Korea. “He really just wants to emerge from the summit as saying, ‘I got them to do what no other president could,’ and I think then he will probably lose interest.”

“The less President Trump is involved in that process,” Ms. DiMaggio said, “the better.”

A vague promise to denuclearize would probably disappoint many in Washington, where there are memories of the North Koreans’ reneging on deals before. It would also fall far short of the demands of hawks like John R. Bolton, Mr. Trump’s national security adviser, who has called for total and immediate denuclearization. And having recently pulled out of the Iran nuclear accord because it was a “horrible one-sided deal,” Mr. Trump has set expectations that he could get a better agreement from North Korea.

Some analysts said North Korea was also unlikely to be satisfied by vague proclamations. Mr. Kim is likely to demand a clear guarantee that the United States would never attack, as well as quick relief from international sanctions.

Mr. Trump has praised those sanctions for bringing Mr. Kim to the table in the first place. But even if Mr. Trump tries to hold firm on them, analysts said, he may already have lost that leverage, as both South Korea and, more crucially, China have indicated that they are willing to lower the pressure on the North.

The North “will count on the fact that they have opened up a track with the Chinese and the Chinese are not in a favorable mind towards Trump right now,” said Christopher R. Hill, who negotiated with Pyongyang for several years during the George W. Bush administration. “There’s a problem with U.S.-Chinese relations that the North Koreans will seek to exploit in the coming months.”