WASHINGTON - The United States hopes to take the reins of international efforts to battle global warming next week with a meeting of major economies aimed at facilitating a U.N. pact to cut greenhouse gas emissions.

President Barack Obama, a Democrat who took office in January, called the meeting last month to relaunch a process that began under his Republican predecessor, George W. Bush, whose commitment to curbing climate change was viewed with skepticism by much of the world.

The stakes are higher now. The Kyoto Protocol, which caps greenhouse gas emissions, runs out in 2012 and leaders from around the globe will gather in Copenhagen in December to forge a successor treaty. Environmentalists hope renewed engagement by the United States and Obama's push for U.S. leadership on the issue will result in a deal.

The White House views next week's forum, which groups 16 major economies including the European Union and the United Nations, as an avenue toward securing a broader pact -- a goal that many believed Bush did not share.

The Bush administration obviously had a completely different approach to this issue than we do, Todd Stern, the U.S. Special Envoy for Climate Change, told Reuters, adding Obama wanted to invigorate the forum with more substance.

They were not fundamentally looking for an international agreement, he said of the Bush administration. We are looking for an international agreement and we're looking for cooperation at a significant, we hope, transformative level.

Bush began the major economies forum in 2007, but the initiative was marred by concern among participating countries that he was trying to circumvent wider United Nations talks.

Nobody took him seriously because he spent eight years pretending climate change didn't exist, said David Bookbinder, chief climate counsel for environmental group Sierra Club, referring to Bush.

Obama, on the other hand, obviously is taking climate change very, very seriously and wants, reasonably enough, to talk to everyone about what to do ahead of Copenhagen.

FACILITATING U.N. TALKS

James Connaughton, a former top environmental adviser to Bush, said the former president's motives were also focused on facilitating a U.N. pact.

The point of this was to be able to inform and help accelerate progress in the UN, he told Reuters.

Obama hopes to cut U.S. emissions by roughly 15 percent by 2020 -- back to 1990 levels -- tougher than Bush, who saw U.S. emissions peaking as late as 2025.

European governments and many environmentalists want Obama to go further.

Energy Secretary Steven Chu indicated on Saturday in Port of Spain, Trinidad, that Washington was not interested in retooling its percentage goal for 2020.

I think that rather than debating a few percent, the best thing we can do is to get started as soon as possible, he told reporters at the Summit of the Americas.

But the April 27-28 meeting, and follow-ups in other countries, are expected to pave the way toward Copenhagen and work out some of the disagreements that remain.

The major economies include: Australia, Brazil, Britain, Canada, China, the European Union, France, Germany, India, Indonesia, Italy, Japan, Korea, Mexico, Russia, South Africa and the United States. Denmark, which is hosting the U.N. meeting in December, was also invited.

The presence of the major economies forum increases our chances of success for getting an agreement at Copenhagen, said Annie Petsonk, international counsel for the U.S.-based Environmental Defense Fund.

The more that those countries can come together around a framework, the greater likelihood that they can pour that into a larger agreement.

One stumbling block, however, may lie with some poor countries and other developing nations not present and what contribution will be demanded from them.

We do not see the most vulnerable countries included in these discussions and that is what we would like to see, said Kim Carstensen, head of environmental group WWF's Global Climate Initiative.