BALI, Indonesia - In a largely symbolic duel over numbers at the U.N. climate conference yesterday, the United States refused to agree that future talks should consider a specific range of targets for sharp cuts in greenhouse-gas emissions.

A proposed text for the Bali conference's final document notes - in a nonbinding way - a widely accepted view that reductions of 25 to 40 percent in richer nations' emissions would be required by 2020, and even deeper cuts later, to head off the worst of global warming.

"It's important to give a clear signal that that's where industrialized countries intend to go," said the U.N. climate chief, Yvo de Boer.

The European Union, which pushed for this mention of potential targets, has itself committed to 20 to 30 percent reductions below 1990 levels by 2020.

But the chief U.S. negotiator said that, because of "many uncertainties," raising such specific numbers would limit the scope of future talks.

"To start with a predetermined answer, we don't think is an appropriate thing to do," Harlan Watson said.

The United States is expected to win out, since Bali's decisions require consensus, and the final "Bali road map" is expected to be what has been long anticipated - a vague, broad mandate for two years of talks on an agreement to succeed the Kyoto Protocol when it expires in 2012.

The United States is the only major industrial nation to reject Kyoto, and the rest of the world hopes to enlist the country in the next phase of binding greenhouse-gas reductions.

The talks here, in the second of two weeks, are expected to intensify with today's arrival of U.N. Secretary-General Ban Ki-moon, who has made climate his top priority, and Australia's new prime minister, Kevin Rudd, who reversed his country's stand and ratified Kyoto last week.

Sen. John Kerry (D., Mass.), a longtime supporter of action on climate change, flew to Bali for a day's rapid-fire meetings yesterday. He told delegates he expected a new president in the White House in January 2009 to end U.S. isolation on climate.

In Washington, congressional Democrats released a report asserting that the White House had systematically tried to manipulate the science of climate change.

Republicans called the report, issued by Rep. Henry A. Waxman (D., Calif.), a "partisan diatribe" against the Bush administration.

The report, which followed 16 months of investigation, relies on hundreds of internal communications and documents, as well as testimony at two congressional hearings, to outline a pattern in which government reports were edited to emphasize the uncertainties surrounding global warming, according to Waxman.

Many of the allegations of interference dating back to 2002 have surfaced previously, although the report by the Democratic majority of the House Oversight and Reform Committee sought to show a pattern of such conduct.

The report said the White House over the years has sought to control public access to government climate scientists, suppressed views that conflicted with administration policy, and extensively edited government reports "to minimize the significance of climate change."

The White House called the findings "rehash and recycled rhetoric."