In a rare address to a joint session of the US Congress, German Chancellor Angela Merkel offered a heart-felt appeal, comparing the battle against climate change to the struggle to bring down the Berlin Wall two decades ago this week.

"I'm convinced that once we in Europe and America show ourselves ready to adopt binding agreements, we will also be able to persuade China and India to join in," Merkel said, backing Western calls for emerging nations to do more.

But her pitch came just hours after Republican senators shunned a critical meeting on a bill -- backed by President Barack Obama -- to set the first US requirements on curbing carbon emissions blamed for global warming.

Asked what impact Merkel's speech might have on the US debate, Senator James Inhofe, the top Republican on the committee looking at the climate legislation, said: "None whatsoever."

Democrat Ben Nelson was similarly blunt, answering the same question with a simple "no."

European Commission head Jose Manuel Barroso, who was also visiting Washington, said he was "worried" by the lack of progress in climate negotiations ahead of the December 7-18 climate meeting in Copenhagen.

"Of course we are not going to have a full-fledged binding treaty, Kyoto-type, by Copenhagen," Barroso told reporters. "This is obvious. There is no time for that."

The summit in the Danish capital had been set up to seal a treaty to succeed the landmark Kyoto Protocol, whose obligations to cut carbon emissions expire in 2012.

Barroso said a meeting next year in Mexico could finalize a treaty but said that Copenhagen needed to come up with the framework of the deal, and that the world's largest economy in particular should take a lead role.

"What we are asking is the United States to show leadership in this, such an important issue," Barroso said.

He warned against a protracted process of negotiations akin to the stalled Doha round of global trade liberalization talks.

"I think it is important not to give up before, because if we start... now to speak about Plan B in Copenhagen we'll probably end in Plan F for failure."

"Let's not do to Copenhagen what has been happening with trade in Doha, where systematically every year we are postponing."

Prime Minister Fredrik Reinfeldt of Sweden, which holds the EU presidency, said that the United States should at least agree on targets for cutting emissions and on financing for developing nations.

"I said that we need to have a clear commitment on targets and on financing coming from the United States," Reinfeldt, who met Obama on Monday, told AFP after talks with key senators.

"We can understand if it's not possible to have everything in place exactly now. But we want a full agreement in Copenhagen and we are able to work through details in the months that come after Copenhagen," he said.

He spoke as pre-Copenhagen negotiations were underway in Barcelona, Spain, where divisions again ran deep between key developed nations and emerging economies.

An EU summit last week agreed that developing nations will need 100 billion euros (146 billion dollars) per year by 2020 to tackle climate change, but failed to nail down how much it would give.

The US role in Copenhagen is overshadowed by the debate in Congress.

The House of Representatives in June narrowly passed the plan to curb carbon emissions but the bill -- already criticized by other developed nations as not ambitious enough -- is bogged down in the Senate.

Some Republicans, like former president George W. Bush, resist action on climate change as too costly to the economy and demand further commitments by emerging nations.

Senator George Voinovich, alone among Republicans in showing up to Tuesday's Environment and Public Works Committee meeting, said the party needed a "full analysis" of the legislation by the federal watchdog, the Environmental Protection Agency.

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