The US has given up hope of reaching a global climate change treaty at Copenhagen and is working towards a deal late next year, the Obama administration said today. The decision ends hopes of a legally binding deal being sealed next month.

"We have to be honest in the process and deal with the realities that we don't have time in these four weeks to put the language together and flesh out every crossed t and dotted i of a treaty," said John Kerry, who chairs the Senate foreign relations committee.

Todd Stern, the state department climate change envoy, agreed. "It doesn't look like it's on the cards for December," he said. "We should make progress towards a political agreement that hits each of the main elements."

The scaling back of US ambitions follows a growing international consensus that a binding legal agreement on global warming could not be reached at Copenhagen – now just 32 days away. The US shift resets expectations for what will be accomplished at Copenhagen, once billed by the UN as a last chance to avoid catastrophic global warming.

Stern, in comments to the house foreign relations committee today, said his comments playing down prospects for a binding treaty at Copenhagen reflected the views of senior US politicians including Ed Markey, the author of a climate change bill passed in June. Stern insisted that negotiators were intent on producing a blueprint in Copenhagen that would lead to a binding legal agreement "perhaps next year or as soon as possible".

He said: "We want something beyond certainly a declaration that we are going to keep working on this. We want a real agreement." However, the UN secretary general, Ban Ki-moon, said today that a delay of a year before a legally binding treaty was signed would be too long, given the threat posed by greenhouse gas emissions.

Kerry, speaking at a National Journal seminar, said he was looking for countries to begin to put in place firm commitments at Copenhagen that would then be enshrined in international law by the end of 2010. "What I am looking for is a binding and real political agreement where the world comes together in Copenhagen with an agreement for fixed reductions that are measurable, verifiable and reportable Then you set either a June or July date or the Mexico date in December next year and work on the language in that year."

However, Kerry acknowledged even that scaled back notion of success hinged on the US Congress passing a climate change law, which seems unlikely because of strong Republican opposition to the possible costs of emissions cuts.

As chair of the foreign relations committee, Kerry will play a pivotal role in getting any treaty ratified by the Senate. He said he was working with a Republican senator, Lindsey Graham, and the one-time Democrat Joe Lieberman to build support for the bill among Republicans and conservative Democrats. The three were meeting later today with the White House, the energy secretary, Stephen Chu, and the interior secretary, Ken Salazar, to craft a bill that would pass in the Senate — and have the support of the Obama administration.

Kerry said the reduced role for Copenhagen could work out to the world's advantage — allowing extra time for America, China, and the international community to co-ordinate their efforts. "The president can go China next week, sit with the Chinese and make clear what he is prepared to do, make clear what the Senate is prepared do. What the house has done has been made clear. so you are in a range, and the Chinese and everyone else enter into a political agreement which does not have the force of law till a year later," he said.

"We in effect have sealed a deal," he said. "It works out be a fairly logicial step by step incremental process"

In Barcelona, at the last negotiating meeting before Copenhagen, rich countries piled pressure on Africa not to derail the climate talks after the poorest countries in the world shocked the UN by walking out of the official talks, demanding that their concerns be met.

The chair of the Africa group of nations, Kamel Djemouai, was recalled from Barcelona by the Algerian government and other African delegations reportedly received "strong" phone calls from their capitals urging them not to imperil the last negotiations before Copenhagen. Algeria admitted that its negotiator had been recalled but it was denied that this was related to Africa's stand.

The African bloc complained that rich nations' carbon cuts were far too small to avoid catastrophic climate change, and refused to participate until more was done. The move forced the UN to abandon several sessions and reschedule others to give rich countries more time to debate emissions cuts. Countries have agreed to devote 60% of the remaining time to those discussions.

France has been supportive of Africa's position ahead of the climate change talks in Copenhagen. But French negotiators are known to have been angered and dismayed by the African move. "They are shooting themselves in the foot," said one French diplomat.