Pressure at home and abroad is ratcheting on Bush to ease his six-year-long hard line on global warming ahead of the June 6-8 get-together, but the White House has not shifted an inch, concurrent sources say.

At stake in the Baltic resort of Heiligendamm is a kickstart for efforts to frame a successor to the Kyoto Protocol, the UN pact for cutting greenhouse-gas emissions that are damaging the climate system.

Summit host Germany is lobbying Bush to ditch the G8's traditional final-communique fudge and to accept at last that the world is facing an exceptional peril in global warming.

With the exception of the United States, there is also a G8 consensus for endorsing two goals, say the sources.

One is a target of a maximum rise in Earth's surface temperature of two degrees Celsius (3.6 degrees Fahrenheit) as compared to 1990 -- an aim dear to the European Union (EU).

The other goal is to halve emissions of greenhouse gas emissions by 2050 -- an objective that Japan unveiled on Thursday in the runup to the summit.

But sources following the contacts between "sherpas", as the G8 leaders' envoys are known, are gloomy.

"What's worrying is that Americans are requiring amendments [to the draft communique] that strike out all reference to a tolerable threshold for global warming and insist that measures be limited to a technological fix," said one.

Another said discord was so entrenched that some issues "may have to go to the leaders to be resolved" -- a phrase that conjures the scenario of a late-night haggle over textual nuances and punctuation by the heads of the world's most powerful economies.

German Chancellor Angela Merkel on Thursday admitted she was "not sure" about the prospects of a climate deal and pointedly questioned US interest in tackling global warming.

She highlighted the European Union's offer of an emissions cut of 20 percent by 2020, compared to 1990 levels, which could be deepened to 30 percent if other major polluters follow suit.

"At European level, we have managed to send a very clear signal, but at an international level, the interest in the issue is very different. This was clear at the EU-US summit in April."

Bush's biggest foreign ally is British Prime Minister Tony Blair, who tried hard but with meagre success to coax the US president into a big deal on climate change at the 2005 G8 summit in Gleneagles, Scotland.

In an interview with the BBC late Thursday, Blair voiced hope the United States would back a stronger agreement this time.

"I think it is possible that we will see action -- and at least the beginnings of that action at the G8 -- I hope so. That's what I'm arguing for."

Phil Clapp, president of the US organisation the National Environment Trust (NET), described the situation as G8 brinkmanship.

"The Bush administration is playing a game of who blinks first," Clapp said in an interview with AFP.

"The question is: Will Chancellor Merkel and Mr Blair and others stick to their guns and say 'we're not gonna water this down, we'd rather have disagreement' and make it clear they disagree than water it down and reach a minimal statement?"

Elliot Diringer, director of international strategies at US thinktank the Pew Center on Global Climate Change, said he held out negligible hope for any breakthrough at Heiligendamm or at Bali, Indonesia, where talks on the successor to Kyoto after the treaty expires in 2012 run from December 3-14.

"Both domestically and internationally, the administration continues to very strongly resist any move toward the types of mandatory actions needed to significantly reduce emissions and we see no indications that it's likely to shift," he said.

The post-Kyoto talks are mired in problems.

The United States, which abandoned Kyoto in 2001, opposes its approach of emissions caps.

Meanwhile, the big developing countries, China, India and Brazil, are opposed to joining industrialised nations in making targeted emissions cuts, saying this would hit their rise out of poverty.

The big three developing countries will be joined by Mexico and Brazil for talks with the G8 leaders at Heiligendamm.

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