The United Nations on Monday lowered expectations for clinching a legally binding agreement at a UN climate change summit in Copenhagen in December, saying it might take longer to secure a final deal.

For months Secretary-General Ban Ki-moon and other top officials at the United Nations have been urging industrialized and developing nations to overcome their differences so they can "seal the deal" and get a binding agreement in Copenhagen.

But recently UN officials and diplomats have said privately that it is unlikely a legally binding deal on reducing greenhouse gas emissions will be clinched at the Copenhagen summit. They have suggested that the most that could be expected was a nonbinding political declaration.

Related readings: 'Comprenhensive' climate treaty ruled out for Copenhagen Copenhagen climate change conference UN starts climate talks in Poland to seek deal in Copenhagen Danish Ambassador on Copenhagen climate change conference G8 makes scant progress to Copenhagen climate pact Ban's climate adviser Janos Pasztor made clear that the secretary-general was planning for "post-Copenhagen" talks.

He said Ban believes we must "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."

"Climate change is not going to be resolved in Copenhagen in the next few weeks," Pasztor said. "We always knew that. It's a long-term problem that will be with us for many years, if not decades, to come. So Copenhagen has to be a milestone."

Ban told a gathering of business leaders in Seattle that he still wanted a strong result in Copenhagen. "We will do our best and try to have a substantive agreement," he said.

"After Copenhagen we may not expect ... to agree on all elements," he said. "But we should have a broad agreement."

US role crucial in global climate talks

Pasztor expressed concern about a new poll showing that the US public was not convinced that the threat posed by global warming was so dire, despite mounting scientific evidence that carbon emissions are harming the climate and the planet.

Ban has repeatedly voiced his concerns about the United States, which had resisted mandatory carbon emissions limits under former President George W. Bush.

Bush's successor, Barack Obama, has reversed US policy on climate change, voicing support for mandatory emission limits and a carbon emission limit trading scheme.

But draft US legislation on climate change is still not ready for approval, and diplomats and UN officials say that adoption of the new US legislation will be crucial for securing a global agreement on fighting global warming.

Ban said in Seattle that he was "very encouraged by the strong commitment of the Obama administration."

"The (US) domestic legislation may not be specific enough but it can have a huge impact," he added.

Danish Prime Minister Lars Lokke Rasmussen warned international parliamentarians in Copenhagen on Saturday that climate talks have been "painfully slow," saying that they may fail to reach an ambitious agreement in time.

Rasmussen said crucial questions remained unresolved, including the commitment of industrialized nations to mid-term targets to reduce emissions and developing countries' commitments to national steps to curb emissions growth.