The development came as the European Union urged the United States and China to deliver greenhouse-gas emissions targets at the long-anticipated summit, saying their delays were hindering global efforts to curb climate change.

For nearly a year, the Obama administration has indicated it would eventually come up with specific targets for quick reductions in pollution that causes global warming, as part of international negotiations. Those targets will soon be made public, officials said.

A senior administration official, briefing reporters on condition of anonymity, said that all countries, including the United States, "will need to put their emissions targets on the table."

The Obama administration has resisted talking specific numbers without the backing of Congress, which is not expected to pass climate legislation until next year at the soonest. The official would not offer details about the U.S. targets but said that any U.S. goal would reflect the unfinished state of legislation on Capitol Hill and would not seek to get ahead of it.

A House-passed bill would slash heat-trapping pollution by 17 percent from 2005 levels by 2020. A Senate bill seeks a 20 percent reduction over the next decade, but that number is likely to come down to win the votes of moderate Democrats.

A panel of U.N. scientists has recommended that developed countries cut from 25 percent to 40 percent of greenhouse-gas emissions by 2020 to avoid a catastrophic rise in sea levels, harsher storms and droughts, and climate disruptions.

President Obama is still considering attending the climate conference in Copenhagen. His decision is expected to be announced within a few days.

The United States has historically been the world's largest greenhouse-gas polluter until China zoomed ahead in 2006. Two weeks before the U.N.-sponsored conference, the world's two biggest polluters have not put any firm bids, or proposals, on the table.

"Without a bid from the U.S. or China, only half of emissions are covered," Swedish environment minister Andreas Carlgren said after talks with other EU nations. He said an agreement was "totally dependent" on both countries promising cuts.

Chinese President Hu Jintao said last week that nations would each do what they were able to do, referring to China's view that developing nations should not be required to make cuts. China has promised to curb emissions but has not said by how much.

World leaders are no longer expected to reach a legally binding agreement in Copenhagen and are aiming instead for a political deal that includes commitments on reducing emissions and financing for developing countries to deal with climate change.

In Geneva, Switzerland, yesterday, a U.N. weather agency reported that greenhouse gases in Earth's atmosphere had reached record highs in 2008, with carbon dioxide levels increasing at a faster pace.

Michel Jarraud, the weather agency chief, said carbon dioxide, the main greenhouse gas in the atmosphere, was 385.2 parts per million in 2008, up 2 parts per million from 2007. The carbon dioxide content in the atmosphere rose slightly faster in 2008 than over the last decade, when the growth rate was 1.9 parts per million, he said.