President Barack Obama declared on Friday a “meaningful and unprecedented breakthrough” had been reached among the U.S., China and three other countries on a global effort to curb climate change but said much work was still be needed to reach a legally binding treaty.

“It is going to be very hard, and it’s going to take some time,” he said near the conclusion of a 193-nation global warming summit. “We have come a long way, but we have much further to go.”

The President said there was a “fundamental deadlock in perspectives” between big, industrially developed countries like the United States and poorer, though sometimes large, developing nations. Still he said this week’s efforts “will help us begin to meet our responsibilities to leave our children and grandchildren a cleaner planet.”

The deal as described by Mr. Obama reflects some progress helping poor nations cope with climate change and getting China to disclose its actions to address the warming problem.

But it falls far short of committing any nation to pollution reductions beyond a general acknowledgment that the effort should contain global temperatures along the lines agreed to at a conference of the leading economic nations last July.

Mr. Obama suggested on Friday’s agreement among the five key countries would be adopted by the larger summit in its closing hours.

“I am leaving before the final vote,” he said. “We feel confident we are moving in the direction of a final accord.”

If the countries had waited to reach a full, binding agreement, “then we wouldn’t make any progress,” Mr. Obama said. In that case, he said, “there might be such frustration and cynicism that rather than taking one step forward we ended up taking two steps back.”

The limited agreement by the U.S., China, Brazil, India and South Africa reflected the intense political and economic obstacles that had blocked a binding accord to restrict emissions of “greenhouse gases” believed to be causing a dangerous warming of the Earth.

The accord calls for the participating countries to list specific actions they have taken to control emissions and the commitments they are willing to make to achieve deeper reductions.

There would be a method for verifying reductions of heat-trapping gases, a senior administration official said, speaking on the condition of anonymity before Mr. Obama made his comments.

Mr. Obama said the five nation’s pledges would be “subject to an international consultation” that will allow each country to “show the world what they’re doing.”

China’s resistance to a verification mechanism had been one of the major sticking points for the U.S. during the two weeks of climate negotiations here.

“We’re in this together, and we’ll know who is meeting and not meeting the mutual obligations that are set forth,” Mr. Obama said.

As for the U.S., he said, “We will not be legally bound by anything that took place here today,” pre-emptively answering congressional critics who had warned repeatedly that Congress will have the final say in any U.S. emission reduction commitments.

The deal also would provide a mechanism to help poor countries pay for dealing with climate change.

The President had planned to spend only about nine hours in Copenhagen as the summit wrapped up after two weeks. But, as an agreement appeared within reach, he added extended his stay by more than six hours to attend a series of meetings aimed at brokering a deal.

“We are running short on time,” Mr. Obama had told the summit as the clock was running out on its final day. “There has to be movement on all sides.”

He met with other leaders, including Chinese Premier Wen Jiabao.

Late in the evening, Mr. Obama and Secretary of State Hillary Rodham Clinton held talks with European leaders, including British Prime Minister Gordon Brown, French President Nicolas Sarkozy and German Chancellor Angela Merkel. Asked how negotiations were going as he entered the meeting, Obama replied: “Always hopeful.”

The direct talks between Mr. Obama and Wen underscored efforts to resolve differences that represent one of the major roadblocks in reaching a global climate deal. The U.S. has been insisting that China, the only nation that emits more heat-trapping gasses than the U.S., make its emissions-reduction pledges subject to international review.

Hours before his announcement of the limited agreement, without mentioning China specifically, Mr. Obama said, “I don’t know how you have an international agreement where we all are not sharing information and making sure we are meeting our commitments. That doesn’t make sense. It would be a hollow victory.”

Mr. Obama indirectly acknowledged that some nations feel the United States is doing too little to reduce greenhouse gas emissions, and he urged leaders to accept a less-than-perfect pact. Meanwhile, he offered no new U.S. concessions.

“No country will get everything that it wants,” Mr. Obama said.

It’s possible that Mr. Obama’s biggest success here will have nothing to do with the climate. He met with the Russian President and said afterward that the United States and Russia are “quite close” to a new nuclear arms control agreement to replace an expired Cold War-era arms control treaty.

The U.S. commitment to reduce greenhouse gasses mirrors legislation before Congress. It calls for 17 percent reduction in such pollution from 2005 levels by 2020 — the equivalent of 3 per cent to 4 per cent from the more commonly used baseline of 1990 levels. That is far less than the offers from the European Union, Japan and Russia.

Even that target was hard-won in a skittish Congress, and Mr. Obama has decided he can’t go further without potentially souring final passage of the bill, approved in the House but not yet considered in the Senate. He also could imperil eventual Senate ratification of any global treaty that emerges next year.