RUSUTSU, Japan — Calling climate change “one of the great global challenges of our time,” the world’s richest nations and emerging powers joined together Wednesday for the first time to commit themselves to pursue long-range cuts in global greenhouse gas emissions, but were split on how to achieve that goal.

The declaration grew out of an unprecedented meeting that brought together 16 nations and the European Union — a group dubbed the “major economies” — around the issue of global warning. The 16 are the Group of 8 industrialized nations: the United States, Japan, Germany, France, Canada, Italy, Britain and Russia; the Group of 5 emerging economies: China, India, Brazil, Mexico and South Africa; and three other major trading nations: Australia, South Korea and Indonesia.

The session, organized by President Bush, took place here on the northernmost Japanese island of Hokkaido, where leaders of the Group of 8 wrapped up three days of meetings on Wednesday.

On Tuesday, leaders of the Group of 8 pledged to “move toward a carbon-free society” by cutting emissions of heat-trapping gases in half by 2050. But Group of 5 poorer countries refused to sign onto that goal. They are holding out until rich nations like the United States take more aggressive steps to cut pollution over the next decade.

That fissure prevented the 16 countries from “reaching any meaningful understanding” in the special Wednesday session, said one expert, Alden Meyer of the Union of Concerned Scientists. But an environmental campaigner, Phillip Clapp of the Pew Environmental Group, said the declaration helped set the stage for the next American president to grapple with climate change when the United Nations conducts negotiations on a binding treaty in Copenhagen, Denmark, in 2009.

“It is good that the developing countries have embraced the principal of a global target that they will participate in,” Mr. Clapp said. “It would have been better if the United States and the other G-8 countries would have been willing to step up to the plate and make a strong commitment about what they would do over the next 10 years. “

Mr. Bush claimed success.

“In order to address climate change, all major economies must be at the table,” he said before flying back to Washington. “And that’s what took place today.”

But the meetings did not produce a long-term emissions goal accepted by all the countries, rich and emerging, which was the goal the Bush administration had sought since announcing the “major economies” effort last year.

For Mr. Bush, who is trying to salvage his legacy on climate change late in his administration after years of international pressure to take a more aggressive stance, the back-to-back declarations were still an important step. Mr. Bush has long insisted that any international treaty include developing nations like China and India.

“This is an enormous movement for a man who questioned the science on global warming, who was opposed to international treaties and who was opposed to international targets,” said Mr. Clapp, a frequent critic of the president’s policies. “Here he is leading the way trying to get a global target. He’s gotten the developing countries to acknowledge there should be a global goal.”

Beyond climate change, the three-day meeting tackled issues including rising food and energy prices, aid to Africa and the political crisis in Zimbabwe.

Debate over the Beijing Olympics bubbled up on the sidelines, as President Bush, President Nicolas Sarkozy of France and Prime Minister Yasuo Fukuda of Japan all said they would attend the opening ceremonies — a move that drew criticism from human rights advocates.

After Mr. Bush met with President Hu Jintao of China on Wednesday, Mr. Hu thanked Mr. Bush, saying, “I highly appreciated that President Bush has on various occasions expressed his opposition to politicizing the Olympic games.”

Mr. Bush, for his part, said he did not “need the Olympics to talk candidly” with China. What he really wants, he said, is to see the U.S.-China basketball game. “If you could help me get a ticket,” he told Mr. Hu, “I’d appreciate it.”

But climate change dominated the summit agenda. Although the meeting put the United States on record for the first time as embracing a specific long-term goal, environmentalists complained that the declaration by the G-8 did not go far enough.

“Major economies meeting turns into major embarrassment meeting for G-8,” the WWF, formerly the World Wildlife Fund, said in a statement.

Together, the countries that issued the declaration are responsible for more than 80 percent of the greenhouse gas emissions that scientists have said are warming the planet. But there is a dispute between rich and poor nations over how to set targets, and who should bear the brunt of the responsibility.

There is also a dispute over the starting point for the Group of 8 plan to halve emissions by 2050. Advocates say the cuts should be pegged to 1990 emissions levels, but Prime Minister Yasuo Fukuda of Japan, the host of the meeting, told reporters Wednesday that the starting point would be “the recent situation.”

There was no mention of a baseline in the group’s declaration. But Mr. Fukuda said, “I think we have everyone’s understanding on this.”

Many scientists say cutting emissions in half by 2050 is not enough to combat climate change, and that it would take an 80 percent drop from 2008 levels to limit chances of runaway warming and centuries of rising sea levels. Developing countries agree.

Under a proposal put forth by China, India, Mexico, South Africa and Brazil, developed nations would cut emissions between 25 and 40 percent from 1990 levels by 2020. David Doniger, an expert on climate change at the Natural Resources Defense Council in Washington, predicted the two sides could come together, but probably not until a new president is in the White House.

“Working that out is going to be hard,” Mr. Doniger said. “But it’s so much further along than it was two years ago when the U.S. wouldn’t even let the negotiations start, and when the Chinese weren’t ready to say anything except, ‘We’re a developing country, you created this problem, you have to solve it.’ 

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An earlier version of this article misidentified the Chinese leader Hu Jintao. He is the president, not prime minister.