TOYAKO, Japan (Reuters) - US President George W Bush promised yesterday to be constructive in talks on global warming but said a deal was impossible unless fast-growing China and India agreed to limit their greenhouse gas emissions.

Climate change is high on the agenda of the annual summit of the Group of Eight (G8) rich nations that starts today at a luxury hotel on the lush northern Japanese island of Hokkaido.

"I'll be constructive. I've always advocated that there needs to be a common understanding and that starts with a goal," Mr. Bush told a news conference after meeting Japanese Prime Minister Yasuo Fukuda, the host of the three-day summit.

"And I also am realistic enough to tell you that if China and India don't share that same aspiration, then we're not going to solve the problem," said Mr. Bush, who turned 62 yesterday.

China, India and 12 other countries will join the regular members of the G8 - the US, Japan, France, Britain, Germany, Canada, Italy and Russia - for parts of the summit.

Global inflation driven by soaring food and fuel prices will be high on a crowded agenda, as will efforts to alleviate African poverty.

Leaders are also likely to condemn the violence that preceded last month's presidential election in Zimbabwe and will discuss North Korea's nuclear programme.

Developing nations including China and India want rich states to shoulder most of the burden of cutting greenhouse gases under a planned pact to replace the Kyoto Protocol, which expires in 2012.

UN-led talks on a new framework are due to conclude in Copenhagen in December next year.

But wide gaps within the G8 as well as between rich and developing countries have raised doubts about the chances for progress beyond last year's summit in Germany, where G8 leaders agreed to "seriously consider" a global goal of halving greenhouse gas emissions by 2050.

South Africa, which is also at this year's summit, highlighted the divisions by demanding that rich countries go much further and reduce their emissions by 25 percent to 40 percent from 1990 levels by 2020 and by 80-95 percent by 2050.

"Without mid-term targets and without a baseline, the target of 50 percent by 2050 is an empty slogan with no substance," Environment Minister Marthinus van Schalkwyk told reporters.

Japan wants the leaders to agree to the 2050 goal but without specifying a base year.

"Climate change is one of the most serious challenges mankind faces," said Mr. Fukuda, who is hoping to forge a strong summit statement on the issue to hoist his poor poll ratings.

Analysts and diplomats have said that the G8 leaders were likely to craft a fuzzy agreement on a long-term goal to allow Mr. Fukuda to save face, but that real progress will likely have to wait until a new US president takes office in January.

"I don't think we're expecting a deal. That will come under the United Nations' auspices in Copenhagen next year," Canadian Environment Minister John Baird told reporters en route to Japan.

"What we hope is that we can get some momentum toward a solid progress on climate change," Mr. Baird said.

Tokyo and Washington say specific interim targets are not on the table in Hokkaido, although leaders are likely to acknowledge the need for advanced countries to set them.

Flanked by Mr. Bush, Mr. Fukuda said that Japanese and US views on global warming were gradually converging.

"As the chair of this G8, I have been asking for his support and I think he has shown his understanding," the Japanese Prime Minister said.

With the attendance of several African leaders, this is the largest gathering since rich-country summits began at the Chateau de Rambouillet outside Paris in November 1975.

Then, as now, leaders are confronted by a spike in the cost of oil which hit a record high of $145.85 a barrel on Thursday.

Oil has soared 50 percent so far this year.

"Rising oil and food prices are having a serious impact on the global economy and we agreed that prompt steps are needed to tackle that," Mr. Fukuda said.

"Our economy is not growing as robustly as we'd like," said Mr. Bush, who is attending his eighth and final G8 summit.

One difference from the early summits is that security is now stifling.

Japan has mobilised 21,000 police to protect the leaders and prevent thousands of anti-G8 activists who have poured into Hokkaido from disrupting the summit.

Some have taken up residence in three camps near the hotel.

"We feel honoured that my camp was chosen as the site. From what I'm hearing, I support their activity," said Akeji Takai, the owner of one of camps.