The G8 -- Japan, Canada, France, Germany, Italy, Russia, the United Kingdom and the United States -- agreed last year to seriously consider a global goal of cutting emissions by 50 percent by 2050.

Bush said any agreement must include those other countries and not just the leading industrial countries, a key sticking point in the negotiations.

"The first thing is to make sure we get a understanding that all of us need to agree on a long-term goal," Bush told reporters at the White House. "Effectiveness comes when major economies come to the table."

Bush in April called for the United States to halt the growth of emissions by 2025, which sparked global criticism as too small a step. He has also opposed an economy-wide plan to cap carbon dioxide emissions.

"The first step is to agree to a long-term goal," he told reporters. "I've talked to our sherpa about that, and he feels pretty good that people are now coming to the clear understanding that we're going to have to come to a long-term goal."

"Hopefully, we can do it at this meeting," Bush said. "If not, we'll continue to press forward to get it done."

The clock is ticking for a climate deal to succeed the Kyoto Protocol, which expires in 2012. International negotiators at last December's meeting in Bali on climate change agreed to start two years of talks aimed at adopting a new treaty in Copenhagen in late 2009.

The United States has not joined the Kyoto Protocol, saying its requirements to cap the greenhouse gas carbon dioxide would hurt the US economy and give an unfair advantage to fast-developing economies like China and India. (Reporting by Jeremy Pelofsky, editing by David Wiessler)