“Is this impasse the United States’ fault? Of course. But others are at fault as well,” said Dan Becker, director of the Safe Climate Campaign in Washington, citing the opposition of polluting industries and the reluctance of emerging economies to commit to binding curbs on emissions. “We have both the obligation and capability of taking the lead on this issue. The longer we delay, the more extreme the steps that will have to be taken.”

Mr. Obama expressed support on Sunday for a proposal from Prime Minister Lars Lokke Rasmussen of Denmark to pursue a two-step process at the Copenhagen conference.

Under the plan, the 192 nations convening in the Danish capital would formulate a nonbinding political agreement calling for reductions in global warming emissions and aid for developing nations to adapt to a changing climate. The group would also promise to work to put together a binding global pact in 2010, complete with firm emissions targets, enforcement mechanisms and specific dollar amounts to aid poorer nations.

“We must in the coming weeks focus on what is possible and not let ourselves be distracted by what is not possible,” Mr. Rasmussen said in Singapore, making clear he would prefer to lock in the progress that has been made to date and not postpone action until countries are prepared to accept legally-binding commitments.

Although many read the compromise as a sign that the Copenhagen talks were doomed to produce at best a weak agreement, Yvo de Boer, the United Nations official managing the climate negotiations, said the statements out of the Singapore meeting did not limit his ambitions.

“Copenhagen can and must deliver clarity on emission reduction targets and the finance to kick start rapid action,” Mr. de Boer said. “I have seen nothing that would change my view on that.”

Not everyone blames the United States for the apparent deadlock. A European Union official, who asked that his name not be used so he could speak more freely, said that Mr. Obama was moving to use his executive authority to regulate greenhouse gases, but that India and China had delivered little beyond promises.