The U.S. stand had drawn loud boos and sharp floor rebukes - "If you are not willing to lead, then get out of the way!" one delegate demanded - before Undersecretary of State Paula Dobriansky reversed her position, allowing the adoption of the so-called "Bali Roadmap."
The upcoming two years of talks, which will fashion a successor to the 1997 Kyoto Protocol, could determine for years to come how well the world will cut emissions of greenhouse gases blamed for global warming. The move came after a year of scientific reports warning that rising temperatures will cause widespread drought, floods, higher sea levels and worsening storms.
"This is the beginning, not the end," U.N. Secretary-General Ban Ki-moon, who made an urgent plea for progress in the final hour of talks, said in an interview with The Associated Press. "We will have to engage in more complex, long and difficult negotiations."
The document, adopted after contentious all-night talks, does not commit countries to specific actions against global warming. It was limited to setting an agenda and schedule for negotiators to find ways to reduce pollution and help poor countries adapt to environmental changes by speeding up the transfer of technology and financial assistance.
Adoption came after marathon negotiations that appeared on the brink of collapse several times.
European and U.S. envoys dueled into the final hours of the two-week conference over the European Union's proposal that the Bali mandate suggest an ambitious goal for cutting industrial nations' emissions - by 25 to 40 percent below 1990 levels by 2020.
The EU and others said the goals were needed to direct upcoming talks. But the guidelines were eliminated after the U.S., joined by Japan and others, argued that targets should come at the end of the two-year negotiations, not the beginning. An indirect reference was inserted as a footnote instead.
Just when it appeared agreement was within reach Saturday morning, developing nations argued that their need for technological help from rich nations and other issues needed greater recognition in the document.
In an apparent resolution, India and others suggested minor adjustments to the text, backed by the EU, that encouraged monitoring of technological transfer to make sure rich countries were meeting that need. But the United States objected, calling for further talks, and only relented when, in an uproar, delegates by turns criticized and pleaded with Dobriansky to reverse course.
"We would like to beg them," appealed Uganda's environment minister, Jesca Eriyo.
Dobriansky's subsequent acceptance of the changes triggered applause - one of the few times that a U.S. action had won public praise at a conference studded with accusations that Washington was blocking progress.
She told reporters after the adoption that the appeals convinced the U.S. delegation that developing nations did not intend to dilute their commitment to take steps to stop global warming.
"After hearing the comments ... we were assured by their words to act," Dobriansky said. "So with that, we felt it was important that we go forward."
At one point, China also angrily accused the U.N. of pressuring nations to sign off on the text, even as sideline negotiations continued - triggering an emotional spat that ended when tearful and exhausted U.N. climate chief Yvo de Boer was escorted out of the hall.
Participants and environmentalists hailed the final agreement. Still, some critics complained the document lacked specific greenhouse gas cuts for industrialized nations, and did not include strong commitments for rich countries to provide poorer ones with green technology.
Critics of the U.S. cheered the reversal.
"We have learned a historical lesson: if you expose to the world the dealings of the United States, they will ultimately back down," said Hans Verolme, director of WWF's Global Climate Change Program.
For developing countries, the final document instructs negotiators to consider incentives and other means to encourage poorer nations to curb - voluntarily - growth in their emissions. The explosion of greenhouse emissions in China, India and other developing countries potentially could negate cutbacks in the developed world.
The roadmap is intended to lead to a more inclusive, effective successor to the 1997 Kyoto Protocol, which commits 37 industrialized nations to cut greenhouse gases by an average of 5 percent between 2008 and 2012.
The pact, however, has been rejected by the largest producer of such gases, the United States, seriously weakening a punch that scientists agree was already too little to have an impact on the environment. U.S. President George W. Bush has argued that the required gas cuts would hurt the economy, and he opposed the lack of cuts imposed on China and other emerging economies.
Critics - including former Vice President Al Gore, who spoke in Bali on Thursday - accused Washington of stonewalling progress at Bali. But many pointed out that with Bush's departure from office in early 2009, chances were high that the next American president would be much more supportive of ambitious cuts in greenhouse gas emissions.
Another clash at the conference was between rich and poor nations.
Developing nations have demanded that industrialized countries acknowledge their primary responsibility for solving the problem. Poorer countries also fear that they will be forced to sacrifice economic growth for the sake of cleaning up a mess caused by the industrialized world.
Richer nations, meanwhile, are concerned about skyrocketing rates of greenhouse gas emissions in the developing world.
Environmentalists accused the U.S. of trying to wreck future talks.
"The United States in particular is behaving like passengers in first class in a jumbo jet, thinking a catastrophe in economy class won't affect them," said Tony Juniper, a spokesman for a coalition of environmentalists the conference. "If we go down, we go down together, and the United States needs to realize that very quickly."