L'AQUILA, Italy -- Leaders of the world's major economies yesterday formally embraced limiting the rise in the Earth's average temperatures but declined to set numerical targets for reducing the greenhouse gas emissions that cause global warming.

The declaration by the Major Economies Forum on Energy and Climate, a group of 17 countries that account for nearly four-fifths of the world's greenhouse-gas production, reflects a tension between developed and developing countries that is hampering efforts to combat climate change, even as many scientists say the need to address it is becoming more urgent.

"It is no small task for 17 leaders to bridge their differences on an issue like climate change," President Barack Obama, who co-chaired the forum, said on the second day of the three-day meeting.

The countries promised to take verifiable steps to cut carbon emissions and cooperate on funding research to develop clean-energy technologies. They acknowledged a growing scientific consensus that average global temperatures should not rise more than 3.6 degrees above average levels of more than a century ago, before large-scale industrial pollution occurred.

But they would not set long-term goals for reducing carbon emissions or timetables for making the changes necessary to keep temperatures in check. The gulf between the two sides remains wide: Rich countries want poor countries to cut emissions. But poor countries want rich countries to go first, and to subsidize their conversion to fuels that emit little carbon.

"Each of our nations comes to the table with different needs, different priorities, different levels of development," Mr. Obama said. "And developing nations have real and understandable concerns about the role they will play in these efforts. They want to make sure that they do not have to sacrifice their aspirations for development and higher living standards."

Mr. Obama said the growth in carbon emissions comes from developing countries, including Brazil, China and India, making them indispensable to dealing with the problem.

The forum's declaration came one day after leaders of the world's eight largest economies agreed to the goal of reducing their carbon emissions by 80 percent by 2050. But the Group of Eight nations declined to set any more immediate targets for combating climate change, disappointing environmentalists and frustrating leaders of developing countries, who see rich nations as unwilling to make the sacrifices they ask of others.

Environmentalists and developing countries also say rich countries became rich in part by using fossil fuels such as coal and oil to increase industrial expansion and living standards. Developing nations are wary of undercutting their own economic growth by turning away from relatively cheap fossil fuels, the leading culprit in climate change.

China, India and other developing countries say that "if you're not going to really help us, then we're not going to put ourselves on the hook" by agreeing to make specific cuts in emissions, said Alden Meyer, director of strategy and policy for the Union of Concerned Scientists, an advocacy group.

Mr. Obama called on finance ministers from the wealthiest nations to formulate plans for funding worldwide emissions reductions and bring them to a meeting of the Group of 20 countries in Pittsburgh in September. That could provide countries such as Brazil, China, India and Mexico with significant money to help pay for the technology required to reduce emissions.