HEILIGENDAMM, Germany — Leaders of the Group of Eight main industrial nations vowed a renewed global push to fight rising temperatures, while agreeing not to force America and Russia to set targets now for cutting greenhouse gas emissions.

The European Union, Japan, and Canada pledged at the G–8 summit to cut carbon emissions in half by 2050. America and Russia promised to take part in talks on a new international treaty to combat global warming.

“The possibility is here for the first time of getting a global deal on climate change with substantial cuts in emissions and everyone in on the deal,” Prime Minister Blair of Britain told reporters in Heiligendamm, Germany, yesterday.

After giving ground to European critics last week by proposing an international conference to stem man-made pollution that is overheating the earth’s atmosphere, President Bush refused to go further at the G–8.

Mr. Bush’s global warming initiative at first left Europe divided over how to respond, with the summit host, Germany’s Chancellor Merkel, keen to craft a face-saving compromise while France’s President Sarkozy pressed for more American concessions.

Mr. Blair, attending his last G–8 before leaving office, said the American counter-offer on climate change helped foster a “very substantial coming together” among world leaders over how to prevent an environmental disaster.

Ms. Merkel, 52, claimed credit for a diplomatic coup like the one she engineered in March when the 27-nation European Union set tighter targets for cutting greenhouse gases and curbing the use of fossil fuels.

The German leader was counting on a climate-change compromise to salvage a summit colored by rhetorical sparring between a newly assertive Russia and the West and by anti-capitalism demonstrations that degenerated into scuffles with police Wednesday. Protesters made new attempts to blockade the beachfront resort yesterday and Greenpeace boats launched a seaborne appeal for tougher climate-protection steps.

Mr. Bush, meanwhile, sought a measure of credibility on the environment by agreeing to bind the U.S. into talks on a follow- up to the Kyoto protocol — the climate-protection accord he pulled out of after taking office in 2001.

The U.S. is “deadly earnest in getting something done,” Mr. Bush, 60, said yesterday after his meeting with Mr. Blair, 54. He added that unless developing countries such as China and India join the discussion, “nothing is going to happen in terms of substantial reductions.”

Faced with a growing clamor at state, local and corporate level in the U.S. to act against global warming, Mr. Bush launched the U.S. back into negotiations on a tougher climate-protecting accord to replace Kyoto, which expires in 2012.

Ms. Merkel played up the fact that there will be a “clear beginning” and “clear endpoint” to the next set of climate talks, starting in December and with a 2009 deadline for an agreement.

“No one can escape this political commitment — it’s a huge step forward,” Merkel told German television reporters yesterday.

The G–8 groups the U.S., Japan, Germany, France, Britain, Italy, Canada, and Russia. Leaders of developing countries including China, India, and Brazil join for the final session tomorrow.

American opposition to mandatory targets for pollution cuts pitted Mr. Bush against Mr. Sarkozy, who took office last month vowing both to curb global warming and improve ties with the U.S. that were strained by the Iraq war.

Making his G–8 debut, Mr. Sarkozy applauded the communiqué’s reference to targets while regretting that “the U.S. didn’t go that final step.”

John Kirton, a University of Toronto professor who follows G–8 diplomacy, said in an interview yesterday that global targets are inevitable because “it’s pretty clear that a lot of other countries are converging toward 2050 and 50%.”

Mr. Bush’s about-face won him rare praise from some environmental groups. Hans Verolme, director of WWF International’s climate-change program, said in an interview that it “is significant that the U.S. has signed up to this. The agreement does move us a step closer to a cooler world.”

Others, like Oxfam and Greenpeace, remained skeptical. Daniel Mittler, Greenpeace International’s climate expert, said in an interview that the Bush administration “is as far away as ever to agreeing such targets itself.”

Earlier yesterday, Greenpeace loosed 11 rubber dinghies flying “G–8 Act Now” banners off the Baltic coast that briefly intruded into the offshore security zone around the summit site before being turned back by police.