Bush, who left for Europe on Monday, last week unveiled a plan for fighting global warming beyond 2012, saying he wanted the world's top 15 emitters to meet later this year and agree new measures to curb emissions by the end of 2008.

His plan shocked EU leaders, including German Chancellor Angela Merkel who had wanted the G8 leading industrialised countries to reach a deal on similar measures at the summit she will host in the Baltic resort of Heiligendamm.

European Union countries fear the Bush plan could sabotage efforts to produce a successor to the Kyoto Protocol under the auspices of the United Nations. They are hoping to convince Bush to integrate his proposals with the U.N. process.

Speaking in Berlin after a meeting with leading climate experts, European Commission President Jose Manuel Barroso called Bush's proposals a "step in the right direction" but cautioned Washington against going down a separate track.

"It was a good step but I think it is important that the commitment of the United States is not seen to be in parallel or even in contradiction to the global efforts but as a contribution to the efforts that are being planned in the United Nations," said Barroso.

Merkel has pressed fellow G8 countries to back a 50 percent cut in emissions of greenhouse gases by 2050 but acknowledged over the past week she is unlikely to overcome U.S. objections to such a step.

European and U.N. officials hope the Group of Eight (G8) -- Britain, Canada, France, Germany, Italy, Japan, Russia and the United States -- can avert failure by giving political impetus for December U.N. climate talks in Bali, Indonesia.

They want to launch talks in Bali on extending and expanding the Kyoto Protocol.

HEATWAVES

Kyoto, which Bush rejected in 2001, is meant as a first step to fend off projections of ever increasing heatwaves, floods and rising seas linked to rising emissions of greenhouse gases, mainly from burning fossil fuels.

It obliges 35 rich nations to cut emissions of greenhouse gases by 5 percent below 1990 levels by 2008-12. Bush said it would cost too much and wrongly omitted developing countries.

Yvo de Boer, the U.N.'s top climate official, acknowledged the G8 was unlikely to agree on the firm emission reduction targets Merkel had pushed for, but said the summit could still be a success in moving the climate debate forward.

"I still think that this G8 can fulfil a very important role," he said, suggesting leaders could agree on a need to launch negotiations in Bali for sharp emission cuts, based on the latest scientific findings about warming.

He said the G8 summit declaration should state clearly that U.S. plans were "complementary" rather than a rival track to the United Nations.

Hans-Joachim Schellnhuber, head of a top German climate research institute and an adviser to Merkel, echoed that view.

"It would be really problematic to invent something new outside the U.N. process," he said. "Under no circumstances can the U.N. process be brought into question."

Merkel received backing for her push from top British, French and Canadian officials.

An aide to Canadian Prime Minister Stephen Harper, who met the chancellor in Berlin ahead of the summit, told reporters: "We're closer to Merkel than to Bush on this issue."

China, the world's number two emitter of greenhouse gases behind the United States, also issued a climate change plan. The plan vows to combat global warming through energy saving, agricultural adaptation and forest planting.