The world can still agree a deal in December to curb greenhouse gas emissions and prepare for a warmer world, co-chairs of a meeting of major polluters in London -- Britain and the United States -- said on Sunday, Reuters reported.

Skeptics argue a U.N. December deadline is now too tight as negotiators have so far failed to agree targets to cut greenhouse gas emissions and funds to help developing countries prepare for more extreme weather and rising seas.

But Britain and the United States pointed to moves from both developed and developing countries including India, Indonesia, Japan and China.

"You can look at that and conclude, as I do, there's a deal to be had," said Washington's top climate envoy Todd Stern, at the start of the October 18-19 talks among major polluters.

"I think a deal is quite possible. There are difficulties, but on the other hand not that many elements to put together a basic deal," he said, adding he was still aiming for December.

The London meeting is the latest in a series of U.S.-initiated "major economies forum" (MEF) sessions, meant to support U.N. talks to agree a new pact to extend or replace the existing Kyoto Protocol at a December 7-18 meeting in Copenhagen.

Among proposed action, last month Indonesia said it would cut greenhouse gases by a quarter compared with current trends by 2020. Chinese premier Hu Jintao said Beijing would curb carbon emissions growth.

Japan's new government committed to a far more ambitious climate target than the previous administration.

"There are good straws in the wind," British energy and climate secretary Ed Miliband told the BBC on Sunday.

But Miliband also pointed to the two biggest obstacles to a deal -- agreeing targets to cut greenhouse gas emissions by rich nations by 2020, and funds to help developing countries.

"There are also some big obstacles that have to be overcome. We need a (emissions target) number from the United States."

Co-chair of the London meeting, Stern told reporters the U.S. 2020 emissions target was "pretty clear," and added a deal would "undoubtedly" include numbers on climate finance for developing countries.

But he could not confirm that the United States would offer concrete numbers for either in Copenhagen.

Under a domestic legislative process, the U.S. House of Representatives had approved a 2020 target to curb U.S. greenhouse gas emissions by 17 percent compared with 2005 levels, and the Senate was considering 20 percent, he said.

U.S. President Barack Obama had previously supported 14 percent, said Stern, who acknowledged his country had to wait for Congress to establish a firm position.

"The range we're talking about is pretty clear but I'm not going to speculate, I am hopeful that things move pretty far down the track, we'll just have to see where we are when December comes around. It isn't a huge big mystery, the number."

Analysts doubt Obama will sign a domestic bill by December. The U.S. offer on climate finance was also "wrapped up" in the domestic climate bill process, Stern said.

Indian environment minister Jairam Ramesh told Reuters on Friday a deal may miss the December deadline by several months. The chair of a U.N. panel of climate scientists, Rajendra Pachauri, said last week the world had the option of meeting again in mid-2010.