With just hours left before the scheduled end to the 12-day parley, the US delegation on Friday had to decide whether to back or oppose a proposal put forward by Canada, the conference host.
A draft of the document obtained by AFP describes climate change as "a serious challenge that has the potential to affect every part of the globe".
It calls for "a dialogue on long-term cooperative action" under the UN Framework Convention on Climate Change (UNFCCC), the offshoot of the 1992 Rio Summit.
It makes no specific reference to the key UNFCCC treaty, the Kyoto Protocol, which spells out action on tackling greenhouse gas pollution.
The "dialogue (would be engaged) without prejudice to any future negotiations, commitments, process, framework or mandate under the UNFCCC," the document stresses.
Agreement on the text was reached by a core group of negotiators pre-dawn Friday, but the US was absent.
Some sources said earlier that Saudi Arabia was also absent, but this was contradicted later by others who said that the Saudis were in fact present and did not object to the deal.
Montreal's summit heard public
calls to prevent global warming
The big question was whether the US would accept the document when the text was put to the conference later on Friday, the sources said.
"We still have a problem," a UN official said, referring to the US.
On Wednesday, the US expressed deep hostility to an earlier version of the proposal and said it would not shift from its belief that a voluntary approach, helped by smart technology, was the answer to tackling global warming.
Adding to the potential for US objections, former US president Bill Clinton, who signed Kyoto for the US and is a hero to some green groups, was to attend the conference in a side event hosted by the City of Montreal.
And the Canadian press reported on Friday that the US delegation was livid with a jab directed at Washington on Wednesday by Canadian Prime Minister Paul Martin, who called on the US to hear the "global conscience" on global warming.
US President George Bush's administration walked out of the UN's Kyoto Protocol on curbing greenhouse-gas pollution in 2001.
It said the cost of meeting the treaty's legally binding caps on these emissions was too costly for its economy.
US delegates have yet to sign on
the summit's final declaration
Kyoto's present commitment period runs out in 2012, but its outcome will at best make only a tiny advance against what is a gigantic problem.
Almost as important as US participation is to get highly populous, fast-growing developing countries, such as China (the world's No 2 polluter) and India, in a closer cooperation.
Under the present Kyoto format, only industrialised countries that have ratified the accord have to make specific emissions cuts in greenhouse gases.
Moving away from fossils carries an economic price because of the need to improve fuel efficiency and switch to technology that may be cleaner but is also more expensive and largely untested.
The ministerial level meeting culminated a 12-day gathering that has drawn 8700 participants.