Japanese Prime Minister Yasuo Fukuda wants to boost momentum for UN-led talks on a new framework beyond limits agreed under the Kyoto Protocol, which expire in 2012. Those negotiations are due to conclude in Copenhagen in December next year.

An agreement by 2009 would give certainty to investors wanting to switch to cleaner energy technologies, as well as to participants in growing carbon markets.

The 71-year-old Japanese leader, whose ratings are languishing at around 25 percent on doubts about his leadership, also needs a successful summit to dampen speculation that his party will dump him when the diplomatic pageantry ends.

A general election must be held by late next year.

"The worst scenario is to have no agreement of any kind that the G8 and MEM can explain to the outside world. When leaders meet, you don't do that," Koji Tsuruoka, director general for global issues at Japan's foreign ministry, told Reuters.

"If you come up with a very empty document that says nothing, this would be faulted as the chairman's lack of leadership, although it may not necessarily be the chairman's fault."

PRE-SUMMIT HAGGLING

G8 leaders agreed last year in Germany to seriously consider a global goal of halving greenhouse gas emissions by 2050.

Climate campaigners say this year's summit should go further by endorsing that goal, compared to 1990 emissions levels, and linking it to bold and specific mid-term targets for developed countries.

But bickering among G8 members and between advanced and developing countries has raised doubts about how much the leaders can achieve next week.

"The G8 countries could certainly take a leadership stand and agree to that (a long-term goal), but I think that really depends on whether Bush is ready to take that leap or not," said Jennifer Morgan, director for climate and energy security at Berlin-based think tank E3G. "Up to this point in time, the US has shown no flexibility on this point."

Europe wants the G8 to commit to a goal of halving by mid-century the emissions that cause global warming, compared with 1990 levels.

Japan is urging the leaders agree to a common vision of a 50 percent cut by mid-century, without specifying a base year.

The Bush administration, though, says it will only set targets if emerging economies such as China are on board.

Both Tokyo and Washington also insist specific interim goals for advanced countries to their reduce emissions by 2020 -- seen by European countries, developing countries and environmentalists as a vital step -- are not on the table in Hokkaido.

SEEKING SUCCESS

Despite the pre-summit haggling, world leaders' traditional tendency to seek an outcome they can pitch to the public as success means a deal could yet emerge, diplomatic experts said.

"There will be some sort of agreement on a long-term goal," said Kuniyuki Nishimura, research director at Mitsubishi Research Institute. "It will be very diplomatic language, but they will agree and present it to the outside as success."

Nishimura said he expected the G8 leaders to agree that the world should strive toward a goal of halving global emissions by 2050, while the rich countries also show their willingness to provide funds to help developing economies restrain growth in their own emissions and adapt to climate change.

Expectations of agreement on firm targets for developed countries to cut emissions by 25-40 percent by 2020 have faded since Fukuda ruled out such commitments last month, but the G8 is likely to acknowledge the need to set such targets soon.