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

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 have been nowhere near enough to avoid catastrophe, and that world leaders need to take part in the 192-nation conference 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 pact in which rich nations would pledge to reduce emissions and finance aid to help the world's poorest cope with the effects of rising temperatures.

Under such a deal, nations would agree to stick to their promises while negotiating the treaty, taking up to a year.

At least 40 leaders are expected in Copenhagen, including British Prime Minister Gordon Brown and French President Nicolas Sarkozy. Possible attendees include President Barack Obama, President Luiz Inacio Lula da Silva of Brazil and Chancellor Angela Merkel of Germany.

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 global regulation, which would hinder the ability of industry to plan future business.

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 3.8 degrees Fahrenheit above its average temperature before the industrial era began 150 years ago.

Any higher rise could trigger a climate catastrophe.