UNITED NATIONS — Just weeks before an international conference on climate change, the United Nations signaled it was scaling back expectations of reaching agreement on a new treaty to slow global warning.

Janos Pasztor, director of the secretary-general's Climate Change Support Team, said Monday "it's hard to say how far the conference will be able to go" because the U.S. Congress has not agreed on a climate bill, and industrialized nations have not agreed on targets to reduce their carbon dioxide emissions or funding to help developing countries limit their discharges.

Secretary-General Ban Ki-moon has made a new climate treaty his top priority, hosting a Sept. 22 summit on climate change to spur political support and traveling extensively to build political momentum for a global agreement to replace the 1997 Kyoto Protocol which only requires 37 industrialized nations to cut emissions.

Pasztor told a news conference "there is tremendous activity by governments in capitals and internationally to shape the outcome" of the climate change conference in Copenhagen, Denmark, in early December, which "is a good development" because political leadership is essential to make a deal.

But he indicated that Copenhagen most likely won't produce a treaty, but instead will push governments as far as they can go on the content of an agreement.

"The secretary-general believes that we must maintain the political momentum established by the 101 heads of state and government who attended the climate change summit and continue to aim for an ambitious, politically binding agreement in Copenhagen that would chart the way for future post-Copenhagen negotiations that lead to a legally binding global agreement," Pasztor said.

Ban was visiting Seattle on Monday to promote action on climate change. The U.N. chief told a news conference that he still thinks the U.S. can come up with an ambitious measure that will encourage other nations to act on carbon emissions.

"I'm very encouraged by the strong commitment by the Obama administration," Ban said.

Pasztor stressed that there is still a final negotiating session in Barcelona, Spain, from Nov. 2-6 that will be followed by two more weeks of work in Copenhagen. The secretary-general is in close contact with the Danish prime minister and might go to the meeting of Asian and Pacific leaders in Singapore on Nov. 14-15 -- which President Barack Obama plans to attend -- to keep pressing for a global accord in Copenhagen, Pasztor said.

Obama attended the U.N. climate summit, and this week the Senate environment committee will take up its version of a global warming bill which would cut greenhouse gases by about 80 percent by 2050 and require more domestic energy to come from renewable sources.

But with work still to be done on health care and deep divisions in Congress over how to deal with climate change, chances the Senate will pass a climate bill by the end of the year are slim.

Ban said he plans to meet with Senate leaders to encourage passage of the climate bill.

By doing so, the Senate "can have a huge political impact for other negotiators of other counties," Ban said. Many developing countries, such as China and India, "are ready to make some political compromises only if and only when the United States is ready to do that."

Pasztor said a U.S. climate bill is very important because without one, U.S. negotiators in Copenhagen can't negotiate on targets for emissions reductions.

He said two key unresolved issues are agreement on emission reduction targets for industrialized countries and how to finance actions by developing countries to limit their emissions growth and adapt to the effects of climate change.

Developed countries want to provide money for specific actions to curb emissions -- but developing countries say the actions depend on how much money they're going to get, Pasztor said, and that still hasn't been decided.