NEW YORK - World leaders committed to reach a significant agreement for curbing climate-damaging greenhouse gas emissions by the end of the year, but promised few specifics during a one-day UN summit on global warming Tuesday.

The US and China, the world’s two largest polluters, promised to tackle their emissions and tasked each other with doing more to halt the rise in global temperatures.

UN Secretary General Ban Ki-moon warned that negotiations aimed at reaching a new global climate treaty by a December UN summit in Copenhagen were “proceeding at a glacial pace”.

Swedish Prime Minister Fredrik Reinfeldt, whose country holds the European Union presidency, said the negotiations were “close to a deadlock”, yet there was no option but to push forward.

Smaller island nations again warned that their livelihood would vanish if the world’s major polluters couldn’t agree to a deal.

President Barack Obama acknowledged that the US has been slow to respond to the threat of climate change, but said: “This is a new day.

“We understand the gravity of the climate threat. We are determined to act,” Obama said, noting efforts by his administration to reduce vehicle emissions and promote renewable energy.

But the Obama administration could be hamstrung at the all-important Copenhagen summit, scheduled Dec 7-18, as major legislation to curb US emissions has stalled in the Senate. Obama said it was up to all major polluters to take action.

He called on other countries - especially emerging economies such as China and India - to make the commitments necessary to lower their own growing emissions, in order to reach a new global agreement.

“We cannot meet this challenge unless all the largest emitters of greenhouse gas pollution act together. There is no other way,” Obama said.

Chinese President Hu Jintao said his country was determined to lower its burgeoning levels of greenhouse gas emissions, but tasked richer nations with helping the poor adapt without destroying their economies.

“China has taken and will continue to take determined and practical steps to tackle this challenge,” said Hu, who is the first Chinese leader in 30 years to join the annual opening of the UN General Assembly.

“We should combine our efforts to address climate change with those to promote the growth of developing countries,” he said.

The US and Chinese comments in part highlighted the ongoing rift between richer and poorer nations. How much wealthy countries should give developing nations to lower their own emissions has been a key stumbling block to a new global climate treaty.

Developing countries argue it is the industrial world that has caused global warming over the past decades, meaning they should bear the burden for ending it. Wealthy nations argue their efforts will be for naught if growing emitters like China don’t commit to similar curbs.

China has proposed that wealthy nations dedicate one percent of their gross domestic product (GDP) to helping developing countries tackle global warming. The measure has been rejected by the US, which wants emerging economies like China to commit to hard targets for lowering their own emissions.

Hu said his country would work to slow the growth of its emissions by a “notable margin” by 2020. The Asian powerhouse would also increase its share of renewable energy use to 15 percent of the total by that year.

“China stands ready to join hands with all countries to build an even better future for the generations to come,” Hu said.

Ban earlier warned that the worst consequences of climate change were drawing ever closer as he urged world leaders to thrash out an ambitious new global treaty by December.

“Now is your moment to act,” Ban told more than 100 leaders who gathered to discuss curbs to halt global warming. “The fate of future generations, and the hopes and livelihoods of billions today rest, literally, with you.”

Ban, who has made tackling climate change his top priority, is hoping Tuesday’s gathering will inject the political will needed to complete the talks in Copenhagen for a successor to the Kyoto Protocol, the world’s first climate treaty, which expires in 2012.

The summit is billed by the UN as the largest climate summit in history, as 86 presidents and 36 prime ministers debated climate change in a series of roundtables throughout the day. Ban will summarize and publicize their views at the end of the gathering.

The climate summit comes ahead of Wednesday’s annual opening of the UN General Assembly, which brings together leaders from around the world for 10 days of speeches about global issues.