Mr. Bush rejected North Korea's demand for a formal no-invasion treaty, saying, "That's off the table." But he left the door open for a security pledge, agreed to by several countries, that would fall short of an actual treaty.
Nuclear tensions hung over Monday's opening of a 21-nation summit of Asian-Pacific leaders, along with disputes over trade and the U.S. occupation of postwar Iraq. On the economic front, China refused to give ground in a currency argument with Washington.
Mr. Bush was meeting over breakfast Monday with South Korean President Roh Moo-hyun to explore how to end the North Korea impasse. It was at the top of the agenda Sunday when Mr. Bush met with Chinese President Hu Jintao, who pledged to encourage North Korea to return to multiparty nuclear talks soon.
With at least two nuclear weapons in its arsenal, North Korea startled the world last year when it admitted running a secret weapons program. In August, talks between the United States, China, Russia, Japan and the two Koreas in Beijing ended without agreement on a next round.
The administration fervently wants to avoid Mr. Bush having a nuclear crisis on his hands as he heads into a re-election battle next year.
Russian President Vladimir Putin said more nuclear talks could yield "good, positive results" if North Korea's security worries were addressed. Japanese Prime Minister Junichiro Koizumi backed the push for new negotiations, while South Korea had no comment on the day's developments.
"I've said as plainly as I can say that we have no intention of invading North Korea," Mr. Bush said after a meeting with Thai Prime Minister Thaksin Shinawatra. "And I've also said as plainly as I can that we expect North Korea to get rid of her nuclear weapons ambitions."
But, he said, short of a treaty, "perhaps there are other ways to say exactly what I said publicly" and to put it on paper "with our partners' consent."
At a photo session with Hu, the Chinese president said only that he would "strive for a peaceful resolution."
North Korea said the meeting in Bangkok was not the place to discuss the nuclear standoff because it "is an issue to be resolved between us and the United States."
But administration leaders, following Mr. Bush's lead, made themselves available on Sunday talk shows to discuss the new proposed approach, described by one official as an "agreement with a small `a."'
"We believe that we could provide the kind of assurances that the North Koreans say they are looking for, without getting it into the formal process of a treaty ... that will require Senate ratification," Secretary of State Colin Powell said on CBS' "Face the Nation."
He made clear the United States wants to first gain agreement from key regional allies before it would go to Pyongyang. "I would not want to prejudge right now what other parties might be willing to do," Powell said in a broadcast interview
Meanwhile, Mr. Bush made little apparent progress in his drive to persuade China to stop a policy that keeps its currency undervalued compared to the U.S. dollar, making Chinese goods less expensive than American products.
Neither Mr. Bush nor Hu directly mentioned the dispute before reporters. However, Hu said, "We both stated our readiness to resolve whatever questions that might emerge in our economic exchange through dialogue."
Privately, Hu told Mr. Bush he agreed that market forces should determine exchange rates, but that to do so too quickly would shock to China's economy, said a senior Mr. Bush official. The official said Hu agreed to set up an "experts group" to study ways China could move more quickly.
But before meeting with Mr. Bush, Hu defended the currency policy, telling international business executives that China's rapid ascendance as a major trading nation was benefiting the world.
With financial commitments from Japan and South Korea in hand, Mr. Bush said he would use the annual Asia-Pacific Economic Cooperation forum here to encourage more nations to be contribute to Iraq's reconstruction. The U.S.-led attack against Iraq was opposed by many nations here, including Russia and Muslim countries.
Mr. Bush, in a speech to troops at the Royal Thai Army headquarters, praised Thailand for sending troops to help with Afghanistan's reconstruction.
"We must stay on the offensive until the terrorist threat is fully and finally defeated," the president said.
Mr. Bush announced the United States and Thailand would begin negotiations on a free-trade agreement and promised to increase U.S.-Thai military cooperation.
Protests in Bangkok were light as world leaders gathered, partly because unprecedented security and government pressure kept demonstrators far away.
Mr. Bush and his wife, Laura, visited the Emerald Buddha, one of the most sacred images in Thailand, marveling at the golden spires and glittering mosaics. "Inspiring," the president said afterward. In the evening, they attended a palace dinner with King Bhumiphol and Queen Sirikit.