U.S., European and other envoys at the U.N. climate conference took an overnight break in final talks early Saturday as they worked to resolve a dispute over how ambitious the goal should be in negotiating future cutbacks in global-warming gases.

U.N. Secretary-General Ban Ki-moon was arriving in Bali later Saturday morning, either to announce the successful launching of the "Bali Roadmap" negotiations, or to help break any lingering impasse.

Yvo de Boer, the U.N. climate chief, said late Friday the talks were going "slower than I had expected" but that he thought the conference was "on the brink of agreement."

"People are working very hard to resolve outstanding issues," he said.

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The negotiating agenda set at Bali, and the results of two years of negotiations to follow, will help determine for decades how well the world can hold down its rising temperatures.

Delegates for days had sparred over the wording of the conference's main decision document, whose most contentious passage was the European Union's suggestion of a goal of reducing emissions by between 25 percent and 40 percent below 1990 levels by 2020.

Trying to break the deadlock, the conference president, Indonesia's Environment Minister Rachmat Witoelar, proposed revised language dropping those mid-range numbers, but still reaffirming that emissions should be reduced at least by half by 2050.

De Boer told reporters the mid-range of 25 percent to 40 percent was implicit — "an inevitable stop on that road" — in the 50 percent goal for midcentury.

Witoelar's proposal provided a basis for the long-expected compromise, producing a relatively vague mandate for two years of negotiations. As worded, his draft "Bali Roadmap" did not guarantee any level of binding commitment by any nation.

On developing countries, the draft would instruct negotiators to consider incentives and other means to encourage poorer nations to curb, on a voluntary basis, growth in their emissions.

De Boer said worldwide public opinion forced the more than 180 national delegations here to find a way to agree. "I don't think any politician can afford to walk away from here," he told reporters.

Including the United States? he was asked. "Perhaps most of all the United States."

The task before the annual assembly was to launch negotiations for a regime of deeper emissions reductions to succeed the Kyoto Protocol, which requires 37 industrial nations to cut output of carbon dioxide and other greenhouse gases by 5 percent below 1990 levels by 2012.

The United States is the only major industrial nation to reject Kyoto. The Bush administration instead favors a voluntary approach — each country deciding how it can contribute — in place of internationally negotiated and legally binding commitments.

For years, the rest of the world has sought to bring the Americans into the framework of international mandates. At this point, however, many seemed resigned to waiting for a change in White House leadership after next November's U.S. election.

In a series of landmark reports this year, the U.N.'s network of climate scientists warned of severe consequences — from rising seas, droughts, severe weather, species extinction and other effects — without sharp cutbacks in emissions of the industrial, transportation and agricultural gases blamed for warming.

To avoid the worst, the Nobel Prize-winning panel said, emissions should be reduced by 25 percent to 40 percent below 1990 levels by 2020.

The Kyoto Protocol nations have accepted that goal, and the numbers were written into early versions of this conference's draft final decision — not as a binding target, but as a suggestion in the document's preamble.

The U.S. delegation immediately opposed any inclusion of such numbers, complaining they would tend to "drive the negotiations in one direction," as U.S. negotiator Harlan Watson put it.

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 the environmentalist coalition here. "If we go down, we go down together, and the United States needs to realize that very quickly."

The draft final document also called for developing countries to take new steps toward restraining growth in their emissions. The exemption of such fast-growing economies as China's and India's from the Kyoto pact was a major U.S. complaint.

Such actions by China, Brazil and others — not envisioned as legally binding by the draft "Bali Roadmap" document — would be key to winning broad acceptance of deeper, mandatory cuts among richer nations.

The EU had threatened to withdraw from separate U.S.-led climate talks if Bali didn't endorse the 25 percent to 40 percent emissions reduction guideline. In those "Major Economies" talks, opened by President Bush in September, Washington is seeking pledges from 16 other nations — responsible, with the U.S., for 80 percent of global emissions — to curtail greenhouse gases according to each country's formula.

The Europeans and others showed little enthusiasm for this "voluntary" approach, and environmentalists denounced it as an effort to subvert the U.N. climate treaty process. It remains to be seen whether EU countries will attend the next meeting, in Honolulu in late January.