Rusutsu, Japan - Pledging to "move toward a low-carbon society," leaders of the world's richest nations on Tuesday endorsed the idea of cutting greenhouse gas emissions in half by 2050, but failed to set a short-term goal for reducing the toxic heat-trapping gases that scientists say are warming the planet.

    The declaration of the so-called Group of Eight - the United States, Japan, Britain, France, Italy, Canada and Russia - called on developing nations like China and India to follow suit.

    It drew immediate criticism from environmentalists, who said it did not go far enough.

    But the leaders themselves cast the announcement as an important step forward in setting the groundwork for a binding international treaty on climate change, which is being negotiated under the auspices of the United Nations with the goal of an agreement by 2009.

    "The G-8 nations came to a mutual recognition that this target - cutting global emissions by at least 50 percent by 2050 - should be a global target," Prime Minister Yasuo Fukuda of Japan said in announcing the agreement.

    Chancellor Angela Merkel of Germany, who has been a major force in driving her colleagues, including President Bush, to take a more aggressive stance on climate change, pronounced herself "very satisfied" in an appearance with Mr. Bush here before the communiqué was announced.

    The leaders are here, on the remote northern Japanese island of Hokkaido, for their annual gathering, and Mr. Fukuda has made addressing climate change a priority for the meeting. On Wednesday, they will meet to talk about climate change again, this time with the leaders of developing nations, including China and India.

    Mr. Bush has insisted that no climate change agreement is workable without the participation of China and India, and the declaration issued on Tuesday agreed. White House officials said they were pleased. Dan Price, Mr. Bush's chief negotiator at the meeting, said the communiqué represented "significant advances in the collective thinking."

    But Phil Clapp, an expert in climate change at the Pew Environmental Group, said the leaders had in fact weakened language they adopted at last year's Group of Eight meeting in Heiligendamm, Germany.

    "The emissions reduction goal is extremely weak," Mr. Clapp said, because it aims to reduce emissions from current levels rather than 1990 levels, as the leaders proposed last year. He added, "The science shows that we have to reduce 80 to 90 percent from current levels to avoid the worst impacts of climate change."

    The United States welcomed the agreement on Tuesday.

    "It has always been the case that a long-term goal is one that must be shared. So what the G-8 has offered today is a G-8 view of what that goal could be and should be but that can only occur with the agreement of all the other parties," said Jim Connaughton, chairman of the White House Council on Environmental Quality.

    But some advocacy groups opposed it, calling it a wasted opportunity and inadequate to meet the challenge of global warming, reflecting their argument that deeper cuts in greenhouse gas emissions should be enforced more rapidly.

    Kumi Naidoo, a leader of an alliance called the Global Call to Action Against Poverty, said in a telephone interview from Japan that the G-8 action was "significantly too slow for us", calling the G-8 negotiations "a battle of words which underscores a lack of political will." He took particular issue with the White House, saying President Bush had "really held back the negotiation, passing the buck to China and India and not accepting that climate change is a catastrophe that the industrialized countries have caused."

    An environmental campaigning group, WWF, said in a statement:" The G-8 are responsible for 62 percent of the carbon dioxide accumulated in the Earth's atmosphere, which makes them the main culprit of climate change and the biggest part of the problem."

    Another key issue in the climate change debate is the extent to which rich countries are prepared to help poor countries meet the costs of adapting their economies to the campaign against global warming.

    The South African environment minister, Marthinus van Schalkwyk, said that "while the statement may appear as a movement forward, we are concerned that it may, in effect, be a regression from what is required," Reuters reported. The G-8 agreement left some latitude for individual countries to set their own targets.

    "The G-8 will implement aggressive midterm total emission reduction targets on a country by country basis," Mr. Fukuda was quoted as saying.

    José Manuel Barroso, the president of the European Commission, called the agreement a "strong signal" and a "new, shared vision," according to news reports from the three-day meeting, which is being held in a mountain-top hotel under the gaze of 21,000 police officers guarding against potential protesters.

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    Sheryl Gay Stolberg reported from Rusutsu and Alan Cowell from Paris.