"Here is the bottom line: we can embrace this accord, take a substantial step forward, and continue to refine it and build upon its foundation," he said.
His comments come after Ban Ki-moon, the UN secretary general, urged world leaders to agree a deal on climate change.
"We are united in purpose. Now it is time for us to be united in action. I implore you to seize this opportunity," he said on Friday.
But Manmohan Singh, India's prime minister, said the summit was likely to fall short of expectations and called for a "genuinely collaborative response to climate change being concluded in the year 2010".
Jonah Hull, Al Jazeera's correspondent in Copenhagen, said it looked as though the summit was "unlikely to come up with anything definitive" on its final day.
Delegates have blamed the US and China for slow progress on a deal, which more than 110 world leaders are expected to sign later on Friday.
Nicolas Sarkozy, the French president, said Chinese objections to a monitoring system for carbon dioxide emissions were a key stumbling block to forging an agreement.
But Wen Jiabao, the Chinese prime minister, defended his country's voluntary climate targets, telling the conference it would meet them with "real action".
Obama and Wen held talks on Friday, making a "step forward" towards a possible climate deal, a US official told the AP news agency.
The two leaders were said to discuss greenhouse gas emission targets, financing for climate aid and transparency in monitoring nations' pledges to cut emissions.
Ailun Yang from Greenpeace China told Al Jazeera that leaders needed to understand that the conference was "too important to fail".
"I think it is very clear that the deal we wanted is already off the table. However I think it is very important for us to get a deal because we will never again have more than 100 heads of state under one roof," she said.
Leaders and senior diplomats from 30 countries crafted a last-minute outline agreement in talks that spilled over into the early hours of Friday.
G77 negotiatior Lumumba Diaping speaks about his expectations from the final negotiations
A European delegate said the draft contained a call to prevent a rise in temperatures of more than two degrees Celsius compared to pre-industrial times, and provides at least $100bn for poor countries to help them cope with the effects of rising temperatures and seas.
But the negotiators failed to agree on the timing and the degree of cuts in greenhouse gas emissions, and stopped short of demands from developing nations, who are calling for a cap of 1.5 degrees Celsius.
Bruno Sekoli of Lesotho, chair of the Group of Least Developed Countries, told the AFP news agency that any rise above the 1.5 C mark would "leave millions
of people suffering from hunger, diseases, floods and water shortages".
Negotiators from 193 nations in total have been trying to hammer out a pact on carbon emissions for the last two weeks, but an agreement has so far proved elusive.
Al Jazeera obtained on Thursday an internal UN document which indicates that even the best pledges being offered to cut emissions may not be enough to curb global warming.
The document, marked confidential and dated December 15 at 11pm, says the cuts offered so far at the summit will not prevent a rise in global temperatures of around 3C.
According to scientists, such a rise would be disastrous, condemning hundreds of millions of people to worsening drought, floods and storms.