New York  - A climate change summit organized by the United Nations on Tuesday will hear from the presidents of the United States and China, who will debut on the world stage on a topic that scientists and politicians still hotly disagree on.

Barack Obama and Hu Jintao will be among eight national leaders to open the one-day climate session at UN headquarters in New York. UN Secretary General Ban Ki-moon will speak first, followed by Rajendra Pachauri, the head of a UN climate change panel.

The eight national speakers on Tuesday will represent all world regions. The US and China are by far the world's biggest emitters of carbon dioxide, which contributes to the rise in global temperatures.

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

The UN secretary general said he hopes the summit will give negotiators their "marching order" to complete talks in Copenhagen in December for a successor to the Kyoto Protocol, the world's first climate treaty, which expires in 2012. The pace of those talks has been slow and painstaking to date.

"The aim of tomorrow's summit is for leaders to mobilize the political momentum that can accelerate the pace of negotiations," Ban said at an event in New York on Monday.

Beijing's foreign ministry said Hu will deliver four major addresses, the first one on climate, while visiting New York and Pittsburgh, Pennsylvania, for a meeting of the Group of 20 (G20) later in the week.

Hu will also be the first Chinese leader in 30 years to address the UN General Assembly, which opens 10 days of speeches by world leaders on Wednesday. Obama will also be making his first address to the assembly since taking office in January.

Hu will reveal China's "new measures" to counter climate change, Beijing's foreign ministry said. China has proposed that developed nations set aside 1 per cent of their gross domestic product (GDP) to help poor countries cut their own carbon emissions.

Cash-rich China may not have any problem. But the one percentage point in GDP would amount to about 140 billion dollars for the US alone, which already expects a budget deficit of 1.58 trillion dollars this year.

The Wall Street Journal said the China Beijing Environmental Exchange plans to launch on Wednesday in New York a voluntary programme to cut carbon emissions. It would urge companies and individuals to follow the example.

Washington, under the Obama administration, has already taken some steps to cut emissions, including those from cars. The US Environment Protection Agency said similar measures could be applied to power plants and other major sources.

Other opening speakers on Tuesday will be newly elected Japanese Prime Minister Yukio Hatoyama, France's President Nicolas Sarkozy, Costa Rica's President Oscar Arias Sanchez, Sweden's Prime Minister Fredrik Reinfeldt, Rwanda's President Paul Kagame and Maldives' President Mohamed Nasheed.

Ban, who has made climate change a crusade, wants governments to agree on the new protocol before Copenhagen, in what the UN calls a seal-the-deal campaign. But the disappointing status of negotiations has discouraged many UN officials.

Ban is banking on Obama to make Copenhagen a success. But US legislation to curb emissions of greenhouse gases has stalled in the US Senate, which could tie Obama's hands when the Copenhagen talks come around in December.  dpa