BONN, Germany (Reuters) - The United States will tell a July meeting of the Group of Eight rich nations that it cannot meet big cuts in emissions of planet-warming gases by 2020, its chief climate negotiator Harlan Watson said.

A protester holds a sign during testimony about the rising cost of gas prices before the Senate Judiciary Committee on Capitol Hill, May 21, 2008. REUTERS/Larry Downing

“It’s frankly not do-able for us,” he told Reuters on Tuesday, referring to a goal for rich countries to curb greenhouse gases by 25-40 percent by 2020 compared to 1990 levels.

A draft summit declaration, dated May 5 and seen by Reuters, showed Washington is blocking efforts to get the summit to agree targets for cutting carbon emissions, insisting that responsibility be shared by big emerging economies.

The European Union says it will cut emissions by 30 percent if other rich countries do and supports a goal of 25-40 percent for all industrialized nations.

But the candidates running to replace U.S. President George W. Bush, and who all support action to stem climate change, were only talking about returning to 1990 or 2000 U.S. emissions levels by 2020, Watson said.

“And I think most analysis of whether we could do that (say) it would be a heavy lift for the United States given our current infrastructure.”

U.S. power production is about 50 percent reliant on high carbon-emitting coal, Watson added.

Watson was speaking on the sidelines of U.N.-led climate talks in Germany. He held out hope for agreement in the July G8 meeting on a global goal to halve emissions by 2050.

“We’d certainly like to get agreement on that, I’m not going to say specific numbers. We’re seriously considering this 50 by 50,” he said, referring to a halving of global greenhouse gases by mid-century, supported by Japan and the EU.

CLIMATE FIGHT

The United States wants all major economies -- code for including big developing countries such as China -- to agree to contribute more to the climate fight, for example funding R&D into clean energy technologies.

Financing such research was currently dominated by the United States and Japan, Watson said.

Talks this week in Bonn are meant to dovetail with the upcoming G8 meeting and a U.S. initiative on the fringes of the G8 involving all major economies, into a U.N. process to agree a new global climate pact by the end of next year in Copenhagen.

A key sticking point in talks is how to split the cost of re-deploying the world’s entire energy system away from fossil fuels, and how soon emerging economies adopt emissions caps.

The present Kyoto Protocol caps the greenhouse gases of some 37 industrialized countries, but not the world’s top two emitters -- the United States and China.

Scientists say that the world must brake and reverse annual increases in greenhouse gas emissions to avoid dangerous climate change including rising seas and more extreme weather.