BARCELONA, Spain -- 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 11th-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.