Mr. Trump later said “a good relationship was formed” with the North Koreans. He plans to meet with Mr. Kim in May or early June, although he warned on Wednesday that he would scrap those plans if it “is not going to be fruitful.”
But Mr. Moon said North Korea was already showing a willingness to make concessions.
“The North Koreans did not present any conditions that the United States could not accept, such as the withdrawal of American troops in South Korea,” Mr. Moon told newspaper publishers in Seoul on Thursday ahead of his planned April 27 summit meeting with Mr. Kim.
“They only talk about an end to hostilities against their country and about getting security guarantees,” he said. “It’s safe to say that the plans for dialogue between the North and the United States could proceed because that has been made clear.”
When Mr. Moon’s special envoys met with Mr. Kim in Pyongyang early last month, Mr. Kim said his country would no longer need nuclear weapons if it did not feel “threatened militarily” and was provided with “security guarantees.”
North Korea issued an official government statement as recently as 2016 calling on Washington to announce the withdrawal of American troops if it wanted to denuclearize the Korean Peninsula.
But a retreat from that demand would not be entirely surprising, according to officials who have dealt with North Korea.
Since the 1990s, North Korean officials have occasionally told the Americans and South Koreans that they could live with an American military presence in the South if Washington signed a peace treaty and normalized ties with the North. Mr. Kim’s father and predecessor, Kim Jong-il, sent Kim Yong-soon, a party secretary, to the United States in 1992 to deliver that message.
When South Korea’s president at the time, Kim Dae-jung, met with Kim Jong-il in Pyongyang in 2000, the North Korean leader was quoted as saying that keeping American troops in Korea for “stability in Northeast Asia” even after a reunification was “not a bad idea, provided that the status and the role of U.S. troops be changed.”
“It is desirable that U.S. troops stay as a peacekeeping force in Korea, instead of a hostile force against the North,” Kim Jong-il said, according to the book “Peacemaker,” by Lim Dong-won, who attended the 2000 inter-Korean summit meeting.
At a forum organized this month by the Seoul-based website Newspim, Mr. Lim said that although North Korea had regularly demanded the withdrawal of American troops, it was important to differentiate its “propaganda policy” from its “real policy.” Mr. Lim, a former unification minister of South Korea, said he believed that the North could accept an American military presence and negotiate away its nuclear weapons if it was offered the right incentives.
But analysts said that even if North Korea accepted an American military presence in the South, it might demand that it be significantly reconfigured and downsized.
In its 2016 statement, North Korea also demanded that the United States stop deploying long-range bombers, submarines and other “nuclear-strike capabilities” in and around South Korea if it wanted a nuclear-free peninsula, a condition that analysts said would doubtless please China.
On Thursday, Mr. Moon dismissed concerns that the United States might end up recognizing North Korea as a de facto nuclear power in return for a promise from it to freeze its nuclear and missile programs.
“I don’t think there is any difference between the parties over what they mean by denuclearization,” Mr. Moon said. “North Korea is expressing a willingness to denuclearize completely.”
In Seoul’s and Washington’s separate planned summit meetings with Mr. Kim, Mr. Moon said there would be “no big difficulties” in reaching “broad agreements in principle” in which North Korea would agree to denuclearize in return for normalized ties with the United States, international aid to help rebuild its economy and a peace treaty to formally end the 1950-53 Korean War. The challenge is in working out a detailed road map to carry out such a deal, he said.
Analysts and former negotiators said the countries would face extremely complicated negotiations on how to verify that North Korea was not cheating on its commitment to denuclearize, as it has been accused of in the past, and on when to provide security guarantees and other incentives. Past agreements to denuclearize North Korea all collapsed in disputes over how to verity a freeze of its nuclear activities.
“As they say, the devil is in details,” Mr. Moon said.