The London-based Financial Times quoted Bush, who has reached Japan, as saying after his meeting with Japanese Prime Minister Yasuo Fukuda that he was prepared to be "constructive" in the discussions on climate change, but insisted that any agreement is contingent on New Delhi and Beijing's participation.
At their meeting in Toyako, the site of the G-8 Summit, Bush was quoted as saying: "I've always advocated there needs to be a common understanding and that starts with a goal. I am also realistic enough to tell you that, if China and India don't share the same aspiration, we're not going to solve the problem."
Bush and Fukuda, both said they would press big developing nations, particularly China, to agree to carbon cuts as part of a global agreement to succeed the Kyoto protocol, which expires in 2012.
China and India, both part of meetings at which climate change will be discussed, have argued that they cannot be expected to cut emissions before they have industrialized.
Although Fukuda has spoken about a convergence of views on climate change, he has also sought to play down expectations of a breakthrough at Toyako.
Experts say any significant agreement is unlikely, largely because the deadline for a post-Kyoto deal is still 18 months away.
Group of Eight leaders, who begin a three-day summit in Hokkaido on Monday, are seeking to advance from last year's commitment at Heiligendamm when they pledged to "consider seriously" halving greenhouse gas emissions by 2050.
Some G-8 leaders would like that statement upgraded to "agree to halve emissions", though the US has been reluctant to commit.
The summit, the biggest in G-8 history with leaders of 14 countries outside the group invited, will discuss what Kazuo Kodama, press secretary of Japan's foreign ministry, described as a "nexus of interrelated issues". These are expected to include rising oil prices, the financial crisis and ways of preventing nuclear proliferation even as the use of "carbon-free" nuclear energy becomes more attractive.