Japan, the host of the three-day Group of Eight summit, pushed for progress in the fight against global warming but environmentalists said that any agreement was unlikely to be far-reaching.

"Yeah, I'll be constructive," Bush told a joint news conference after meeting Japanese Prime Minister Yasuo Fukuda on the eve of the G8 summit in the northern mountain resort of Toyako.

"I also am realistic enough to tell you that if China and India don't share the same aspiration that we're not going to solve the problem," Bush said.

Fukuda said last-minute climate negotiations were underway within the G8, which comprises Britain, Canada, France, Germany, Italy, Japan, Russia and the United States.

"The US, I believe, has not really lost a sense of direction. I think that our views are gradually converging," Fukuda said.

Last year's G8 summit in Germany agreed, under pressure from Chancellor Angela Merkel, that the major economies would "consider seriously" at least halving greenhouse gas emissions by 2050.

The Yomiuri Shimbun said that G8 leaders would this week say they "will take the lead in making efforts to halve" emissions, or something similar.

Europe and Japan want to upgrade the expression "consider" used in Germany to "agree" but the United States remains opposed, Japan's best-selling newspaper said.

The United States is the only major industrial nation to reject the Kyoto Protocol that mandates cuts in carbon emissions, with Bush arguing that it is unfair as it makes no demands of fast-growing emerging economies.

Bush, backed by Canada, has argued that the G8 is not the right forum to discuss what to do after Kyoto's obligations end in 2012 because it does not include developing countries.

However, Japan has invited leaders of eight other major economies including China and India for climate change talks with the G8 on Wednesday.

Developing countries argue that rich nations are historically responsible for climate change and should shoulder the burden.

South Africa, whose President Thabo Mbeki will take part in Wednesday's meeting, said that last year's agreement at the G8 meeting in Germany "lacked credibility" as it provided no figures for the mid-term until 2020.

"Just to say reduction in emissions by 50 percent in our view is an empty slogan," said Marthinus van Schalkwyk, the South African environment minister.

He proposed that rich nations commit to cut carbon emissions by 25 to 40 percent by 2020 -- as proposed by the European Union if other major economies come on board.

"That's what we would like to see as the outcome and that's what we would like to define as an ambitious outcome," Van Schalkwyk told reporters.

But Japan's Environment Minister Ichiro Kamoshita said the host nation was unlikely to volunteer a specific mid-term target in Toyako. Japan has launched a study on mid-term targets to be completed by next year.

Environmentalists said they expected the issue to be a bargaining chip, with developing countries dangling the possibility of long-term commitments if rich nations step forward on mid-term goals.

Climate negotiators largely agree that any agreement on an emissions cut target would come next year after Bush leaves office. Both major candidates to succeed Bush have pledged tougher action to fight global warming.

Some 190 nations including the United States agreed in December in Bali to reach a deal on a post-Kyoto treaty by the end of 2009.

"India and China agreed in Bali that they were ready to move. So what Bush is harping at is a bit out of date," said Antonio Hill, climate change expert at charity Oxfam.

"What we can hope for, though, is that developing countries would be a bit bolder than they were last year," he said.

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