NEW YORK—With roughly a month until the Copenhagen climate negotiations commence, United Nations Secretary-General Ban Ki-moon on Wednesday said he is optimistic world leaders will reach an ambitious agreement despite stalemate over carbon-emission cuts, with the developed countries failing to deliver on issues like setting concrete targets for reduction.

“We are not lowering expectations ahead of the Copenhagen meeting. There is a long way to go still,” Ban told journalists during a press conference here at the UN Headquarters.

For the past few months, Ban has been pressing nations to commit to firm emission limits when they meet in December in the Danish capital to work out a new treaty to slow global warming, replacing the 1997 Kyoto Protocol on carbon-dioxide emissions. The meeting has been billed as a last chance to avoid the impact of global warming. The UN also hosted a September 22 summit on climate change to spur political support to build political momentum for a global agreement.

Despite the gridlock at the last round of climate-change negotiations held in Bangkok earlier this month, Ban had said  that “the elements of a deal are on the table.”

“We need to step back from narrow national interest and engage in frank and constructive discussion in a spirit of global common cause,” the UN chief stressed.

Earlier, Ban said the leadership of the United States in this endeavor is vital, noting that he is encouraged by bipartisan initiative in the US Senate.

This week, the Senate environment committee will take up its version of a global warming bill. The legislation would cut greenhouse gases by about 80 percent by 2050 and require more domestic energy to come from renewable sources.

“We cannot afford another period where the United States stands on the sidelines. An indecisive or insufficiently engaged US will result in unnecessary and unaffordable delays in tackling global warming,” he said.

With the last round of negotiations before the start of the Copenhagen conference kicking off next week in Barcelona, Spain, “we are now at a rather critical juncture,” Janos Pasztor, director of the Secretary-General’s Climate Change Support Team, told journalists here.

“This is a good development as it is only governments who can make the deal and bring us success in Copenhagen,” Pasztor said. “When leaders meet in December, they have the ability to “deliver an agreement on a range of fast-track implementation measures for which credible resources are needed and which governments need to make available.”

To be effective, such a treaty must include carbon emission reduction targets for developed countries by a specific date, some additional mitigation steps by developing countries if technology and finances are made available, a roadmap for adaptation and agreement on financing.

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

He said two key unresolved issues are an 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.

“Developing countries are adamant that we must maintain the Kyoto Protocol with its target. They don’t want to get rid of the Kyoto Protocol until they see that something else is in place that also has targets for the developed countries,” Pasztor said.

Pasztor said that it was difficult to say how far the Conference would go, but that there must be a push for the most ambitious mitigation and financial commitments. Those areas were related, he said, as developing countries maintained that their mitigation efforts were dependent on the amount of financing they received.

He added that developed countries have said they needed to know what mitigation efforts were planned, because how much they could contribute was linked to carbon markets. Political leadership was necessary to make the first step.  British Prime Minister Gordon Brown had made such a move by suggesting $100 billion as a figure to start discussions.