BARCELONA, Spain (AP) - After two years of tough U.N. climate talks often pitting the world's rich against the poor, negotiators said Friday a new global agreement now rides on industrial nations pledging profound emissions cuts next month in Copenhagen.

Negotiators from industrial nations, including the United States, said eleventh-hour promises are possible and a global warming pact can be reached.

But developing countries complained that pledges so far were nowhere near enough to avoid a catastrophe, and that world leaders need to take part in the 192-nation conference on Dec. 7-18 to cut a meaningful deal.

"Part of the frustration is that a deal is so close ... all the elements are there," said Kevin Conrad, the delegate from Papua New Guinea. "But it's absolutely conceivable for senior people to come together and spend a week and clean all this up."

The United States was universally seen as the linchpin to a deal, but it has been unable to present its position or pledge emissions targets because of the slow progress of climate legislation in Congress. "Everyone else wants to calibrate against" the Americans, Conrad said.

With the U.S. position still unclear, expectations at this week's U.N. talks in Spain shifted toward a political agreement in which rich nations would pledge to reduce emissions and to finance aid to help the world's poorest cope with the effects of Earth's rising temperatures.

Under such a deal, nations would agree to stick to their promises while negotiating the treaty, taking as long as a year. If world leaders come to Copenhagen to endorse the deal, those promises would carry more weight, delegates said.

At least 40 leaders are expected, including British Prime Minister Gordon Brown and French President Nicolas Sarkozy.

Former Vice President Al Gore said he believes President Barack Obama will attend, although the White House has not confirmed that. President Luiz Inacio Lula da Silva of Brazil has indicated he may come, and a spokesman for Chancellor Angela Merkel of Germany said she is keeping the date open.

Yvo de Boer, the U.N. official who is shepherding the talks, said negotiators still hoped to achieve a significant agreement setting specific goals.

"Governments can deliver a strong deal in Copenhagen," de Boer said, adding that it would be hard for developed countries "to wiggle out" of any written commitments.

The deal may take the form of consensus decisions, including an overarching statement of long-term objectives, along with a series of supplemental decisions on technology transfers, rewards for halting deforestation, and building infrastructure in poor countries to adapt to global warming, delegates said.

Developing nations were mistrustful of any result that did not hold wealthy nations to legally binding targets, citing past broken promises in development aid and famine relief.

The aim of the negotiations has been to broker an agreement building on the 1997 Kyoto Protocol, which expires in 2012. Without a new one, carbon emissions will have no international regulation, which would hinder the ability of industry to factor in the price of carbon and plan future business.

While some countries, such as Germany and Britain, are meeting their Kyoto emission-reduction targets, others have not. Canada's emissions grew by more than 25 percent from 1990 to 2007, U.N. figures show, although it committed to reduce them 6 percent from 1990 levels by 2012. Japan's grew 9 percent in that period, compared with a target of minus 6 percent.

De Boer was looking to Washington to announce a clear emissions target for 2020, saying "a number from the president of the United States would have huge weight."

"The United States is interested in the strongest possible agreement we can get from this process," said Jonathan Pershing, the chief U.S. delegate to the talks. He showed impatience with developing nations for wanting to hold rich nations to legally enforceable targets while arguing they should be exempt from them.

"We are looking for parallelism. We are not looking for imbalance," he said.

He declined to say whether the U.S. will be ready to submit a target for the Copenhagen accord, adding that Obama has the authority to make a commitment without congressional approval, "but a decision on whether or not we will do it has not yet been made."

U.N. scientists say rich countries must cut carbon emissions by 25 percent to 40 percent from 1990 levels by 2020 to prevent Earth's temperatures from rising 2 degrees Celsius (3.8 degrees Fahrenheit) above its average temperature before the industrial era began 150 years ago. Anything rise beyond that could trigger climate catastrophe.

So far, reduction pledges total 11 percent to 15 percent. But those could be seen as negotiable.

The wider issue of ending the Copenhagen conference without a legally binding agreement disappointed developing nations already suffering droughts, floods and other disasters blamed on rising temperatures. Those countries urged negotiators not to give up on a binding pact in Copenhagen.

South Africa's chief negotiator, Alf Wills, warned against promoting a watered-down text, saying "we will not accept a weak, green-wash outcome."

The European Union said it wanted the most ambitious deal possible. "We are going to change the fundamentals of industrial civilization, so it's no wonder there is a lot of activity going on in a negotiation like this," said Anders Turresson of Sweden.