Confident that governments will reach a climate change deal next month, UN Secretary-General Ban Ki-moon is heading to Washington Tuesday to ensure that the United States is on board.

Ban plans to meet with key senators and White House officials to discuss how governments are approaching the climate negotiations "and what those governments expect, in terms of the role of the United States," the secretary-general's top adviser on climate change said Monday.

Ban and Janos Pasztor, the director of his Climate Change Support Team, were originally campaigning for agreement on a new treaty at Copenhagen. But in the past month, both have scaled back expectations, focusing instead on getting a political deal on the key elements that can be turned into a treaty, hopefully next year.

At the final round of negotiations in Barcelona that ended last week, the United States was universally seen as the linchpin to a political deal, but it has been unable to present its position or pledge emissions targets because of the slow progress of climate legislation in Congress.

Last week, Senate Democrats sidestepped a Republican boycott and pushed a climate bill out of a key committee -- but at least five other committees still must weigh in, and the partisan antics early on threatened to cast a pall over the measure -- one of President Barack Obama's top priorities.

Despite the likelihood that there will be no final action in the U.S. Congress before the 192 UN member states meet in Copenhagen from Dec. 7-18 to try to reach a deal, Ban believes the major outstanding issues can be resolved at Copenhagen.

"The secretary-general is confident that governments will reach agreements in Copenhagen on the fundamental issues that will form the substance of a legally binding international agreement, which is the end goal for guiding action on climate change," Pasztor told a news conference.

Pasztor said Ban's confidence in reaching a political agreement is based on his talks with world leaders, who all want to have a deal in Copenhagen.

"While we're not quite there yet, the willingness is there to make it happen," Pasztor said. "So it's not a question of whether or not we're going to have a deal. It's a question of how we're going to make sure that we get a good deal in Copenhagen, and the secretary-general is convinced that it is possible and therefore it will happen."

The aim of the negotiations has been to broker an agreement building on the 1997 Kyoto Protocol, which expires in 2012. Without a new one, carbon emissions will have no international regulation.

UN scientists say rich countries must cut carbon emissions by 25 per cent to 40 per cent from 1990 levels by 2020 to prevent Earth's temperatures from rising two degrees Celsius above its average temperature before the industrial era began 150 years ago. Any rise beyond that could trigger climate catastrophe, they say.

So far, reduction pledges total 11 per cent to 15 per cent, but those could be seen as negotiable.

Pasztor said the world's major industrialized nations must agree to more ambitious reductions -- and developing countries should also agree on ambitious targets to reduce their growth of carbon emissions.

Rich nations must also take action -- and provide financial support -- to help poorer developing countries limit their emissions and adapt to the effects of climate change including floods and drought, he said.

Pasztor said it was "positive" that finance ministers from the Group of 20 major economic powers said this weekend that they're willing to work for an ambitious deal in Copenhagen.

"What was also clear is that they were not yet ready to sign off on the details," Pasztor said. "They still need to do some homework. ... There's still time for that, not much, but there is still a bit of time."