German Chancellor Angela Merkel, a leading proponent of strong action to confront global warming, gave the Copenhagen Accord grudging acceptance but said she had "mixed feelings" about the outcome and called it only a first step.
Obama's day of frenetic diplomacy produced a three-page document promising $30 billion in emergency aid in the next three years and a goal of channeling $100 billion a year by 2020 to developing countries with no guarantees.
The five-nation agreement includes a method for verifying reductions of heat-trapping gases - a key demand by Washington, because China has resisted international efforts to monitor its actions.
The agreement, which also includes India, South Africa and Brazil, requires industrial countries to list their individual targets and developing countries to list the actions they will take to cut global warming pollution by specific amounts. Obama called that an "unprecedented breakthrough."
"We have come a long way, but we have much further to go," he said.
If the countries had waited to reach a full, binding agreement, "then we wouldn't make any progress," 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."
He suggested the agreement would be adopted by the larger summit in its closing hours. The conference continued into the early hours of Saturday with delegates preparing for a final plenary session.
The emerging outcome was a disappointment to those who had anticipated the Copenhagen Accord would be turned into a legally binding treaty. Instead, it envisions another year of negotiations and leaves myriad details yet to be decided.
Merkel said "the path toward a new agreement is still a very long one." European Commission President Jose Manuel Barroso said the deal was "clearly below" the European Union's goal.
"I will not hide my disappointment," he said.
But British Prime Minister Gordon Brown said the agreement had almost universal support. "Let's remember, a year ago nobody thought this sort of agreement was possible," he said.
Lumumba Di-Aping, the Sudanese ambassador who chairs the bloc of developing countries, called it "extremely flawed."
"A gross violation has been committed today against the poor, against the tradition of transparency and participation of equal footing for all parties of the convention and against common sense," he said, complaining that Obama negotiated the pact in one-on-one meetings and a forum of 25 nations.
The document said carbon emissions should be reduced enough to keep the increase in average temperature below 2 degrees Celsius (3.6 degrees Fahrenheit), which is stronger than in any previous declaration accepted by the rich countries.
However, environmental groups called it a meaningless aspiration.
"The deal is a triumph of spin over substance. It recognizes the need to keep warming below 2 degrees but does not commit to do so. It kicks back the big decisions on emissions cuts and fudges the issue of climate cash," said Jeremy Hobbs, executive director of Oxfam International, an organization that works with developing countries.
He said the agreement "barely papers over the huge differences between countries which have plagued these talks for two years."
Obama spent the final scheduled day of the climate talks huddling with world leaders, including Chinese Premier Wen Jiabao, in a bid to salvage an accord amid deep divisions between rich and poor nations.
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 Obama reflects some progress helping poor nations cope with climate change and getting China to disclose its actions to address the warming problem.
He said the world will have to take more aggressive steps to combat global warming. The first step, he said, is to build trust between developed and developing countries.
"It's not what we expected," Brazilian Ambassador Sergio Barbosa Serra said. "It may still be a way of salvaging something and paving the way for another a meeting or series of meetings next year."
Obama had planned to spend only about nine hours in Copenhagen as the summit wrapped up. But, as an agreement appeared within reach, he extended his stay by more than six hours to attend a series of meetings aimed at brokering a deal.
New Zealand's climate change ambassador Adrian Macey called it "a modest deal."
"I see Kyoto as a first step," Macey said. "This another first step, a global first step."
More than anything, Macey found the U.N. process on climate change "appalling."
John Sauven, executive director of Greenpeace UK, decried that "there are no targets for carbon cuts and no agreement on a legally binding treaty."
The two-week, 193-nation conference has been plagued by growing distrust between rich and poor nations. Each side blamed the other for failing to take ambitious actions to tackle climate change. At one point, African delegates staged a partial boycott of the talks.
Many delegates had been looking to China and the U.S. - the world's two largest carbon polluters - to deepen their pledges to cut their emissions. But that was not to be.
"We are ready to get this done today, but there has to be movement on all sides to recognize that it is better for us to act rather than talk," Obama had said in an address to the conference, insisting on a transparent way to monitor each nation's pledges to cut emissions.
As negotiations evolved, new drafts of the document emerged with key clauses being inserted, deleted and reintroduced with new wording.
In a diatribe against the U.S., Venezuelan President Hugo Chavez criticized the conference as undemocratic.
"There is a document that has been moving around, all sorts of documents that have been moving around, there is a real lack of transparency here," he said earlier Friday. "We reject any document that Obama will slip under the door."
Obama and Wen met twice - once privately and once with other world leaders present - in hopes of sweeping aside some of the disputes that have barred a final deal. Officials said the two leaders took a step forward in their talk and directed negotiators to keep working, but the degree of progress was not immediately clear.
Later Friday, Obama and Secretary of State Hillary Rodham Clinton held talks with European leaders, including Merkel, Brown and French President Nicolas Sarkozy. Reporters asked how negotiations were going as Obama walked into the meeting. "Always hopeful," he replied.
Swedish Environment Minister Andreas Carlgren, negotiating on behalf of the 27-nation European Union, blamed the impasse on the Chinese for "blocking again and again," and on the U.S. for coming too late with an improved offer, a long-range climate aid program announced Thursday by Clinton.
"President Obama was not very proactive. He didn't offer anything more," said delegate Thomas Negints, from Papua New Guinea. He said his country had hoped for "more on emissions, put more money on the table, take the lead."
Find behind-the-scenes information, blog posts and discussion about the Copenhagen climate conference at http://www.facebook.com/theclimatepool , a Facebook page run by AP and an array of international news agencies. Follow coverage and blogging of the event on Twitter at: http://www.twitter.com/AP-ClimatePool