The world is likely to see a comprehensive global warming deal, instead of a political declaration on Dec 18, when the United Nations climate change summit ends.

Leaders from China and the United States yesterday lit up hopes for success at the Copenhagen climate change conference by vowing to look for a comprehensive deal to battle global warming amid dominating expectations that the international community can only achieve a political framework.

US President Barack Obama said the US and China are looking for a comprehensive deal that will "rally the world".

Obama said the goal at the Copenhagen summit should be an agreement that has "immediate operational affect", not just a political declaration.

President Hu Jintao also said the two countries would work together for positive results at Copenhagen next month.

China and the US would cooperate with all sides concerned, on the basis of the "common but differentiated responsibilities" principle and their respective capabilities, to help produce results at Copenhagen, Hu said.

Some experts said the commitments delivered by the two leaders are "positive and encouraging" in the run-up to the summit that begins on Dec 7 amid the judgment that the world needs an extra six months to reach a deal.

"Obama's stance is positive but we must also realize that hurdles are mounting," said Huang Shengchu, climate change expert and president of China Coal Information Institute. "At home, the voices are many and the US should act to remove the hurdles."

Hou Yanli, director of the WWF's Global Climate Initiative in China, said the agreement reached between China and the US will be conducive for the realization of a legally binding accord on the Copenhagen meeting.

"The joint statement brings us more confidence that the international community could achieve a satisfactory result at the Copenhagen meeting," Hou said.