Representative Henry A. Waxman of California, one of several senior Democrats who urged Mr. Obama to raise the issue in these talks, praised the announcement. "A global phase-down of HFCs would eliminate more heat-trapping gases by 2050 than the United States emits in an entire decade," he said in a statement.
Mr. Obama and Mr. Xi also found areas of agreement over North Korea, which under pressure from China has muted a flurry of belligerent statements after nuclear and missile tests this year. After suspending nearly all contact with South Korea, the North has in recent weeks reversed course, and on Sunday officials of the two countries are to meet at a border village to arrange the first cabinet minister-level meeting in six years.
Mr. Obama's administration has welcomed China's new assertiveness with its neighbor and ally, believing that it reflects a new calculation that a constant state of crisis on the Korean Peninsula is destabilizing for the Chinese as well. The two presidents held a long discussion on North Korea over what Tom Donilon, Mr. Obama's departing national security adviser, called "a very lively dinner" on Friday, and he said that they agreed that dealing with the country's nuclear arsenal was a promising arena for "enhanced cooperation."
"They agreed that North Korea has to denuclearize, that neither country will accept North Korea as a nuclear-armed state" and that their two nations would work together to achieve that through pressure on Pyongyang, Mr. Donilon said.
(Read More: Hard Issues On Table at Obama, Xi 'Informal' Summit)
The two presidents met for nearly eight hours beginning Friday evening, and appeared eager to redefine the relationship in a way that would allow their countries to overcome their economic, political and diplomatic differences, rather than letting new — or old — crises derail progress across the spectrum of issues.
On the most contentious issue in recent months — American accusations that Chinese corporations linked to the military had pilfered military and economic secrets and property in cyberspace — the officials seemed to speak past each other. That dominated Saturday's talks here at a secluded estate, but ended without a clear acknowledgment by Mr. Xi of any culpability.
China's state councilor, Yang Jiechi, said China strongly opposed hacking and cyberespionage and was itself a victim, while Mr. Donilon warned that the threat from China threatened to constrain the spirit of partnership Mr. Obama and Mr. Xi publicly declared they wanted.
Mr. Obama warned that if the hacking continued, Mr. Donilon said, it "was going to be a very difficult problem in the economic relationship."
In remarks during a joint appearance on Friday night, Mr. Obama at least publicly softened his language and spread the blame for the hacking and theft of business, financial and military information. "Those are not issues that are unique to the U.S.-China relationship," the president said. "Those are issues that are of international concern. Oftentimes it's nonstate actors who are engaging in these issues as well."
He added, "We're going to have to work very hard to build a system of defenses and protections, both in the private sector and in the public sector, even as we negotiate with other countries around setting up common rules of the road." And, Mr. Obama said, China would face similar threats as its economy develops — Mr. Xi suggested it already had — "which is why I believe we can work together on this rather than at cross-purposes."
(Read Op-Ed: Shelve Diplomacy, Mr. President: Get Tough on China)
Secretary of State John Kerry, who attended the meetings, has previously announced that the two countries would discuss the matter as part of the annual meetings known as the Strategic and Economic Dialogue, to be held in Washington in July.
Mr. Yang said that the two discussed a host of contentious issues and "did not shy away from differences." Mr. Xi called on the United States to end its arms sales to Taiwan, he said, and reasserted its territorial claims, while pledging to resolve them peacefully. Mr. Yang also defended China's control of its currency and said it was not the core trade issue between them.
Broadly, though, both leaders urged cooperation, not conflict. Mr. Obama called for joint efforts to address climate change, including through sharing clean-energy technologies, and to establish better military communications so "that we each understand our strategic objectives at the military as well as the political levels."