Senate Republicans on Friday blocked a global warming bill that would have required major reductions in greenhouse gases, pushing debate over the world's biggest environmental concern to next year for a new Congress and president.

Democratic leaders fell a dozen votes short of getting the 60 needed to end a Republican filibuster on the measure and bring the bill up for a vote, prompting Majority Leader Harry Reid to pull the legislation from consideration.

The Senate debate focused on bitter disagreement over the expected economic costs of putting a price on carbon dioxide, the leading greenhouse gas that comes from burning fossil fuels. Opponents said it would lead to higher energy costs.

The 48-36 vote fell short of a majority, but Democrats produced letters from six senators — including both presidential candidates Barack Obama and John McCain — saying they would have voted for the measure had they been there.

"It's just the beginning for us," proclaimed Sen. Barbara Boxer, D-Calif., a chief sponsor of the bill, noting that 54 senators had expressed support of the legislation, although that's still short of what would be needed to overcome concerted GOP opposition.

"It's clear a majority of Congress wants to act," Boxer said at a news conference.

She and other Democrats said this now lays the groundwork for action on climate change next year with a new Congress and a new president that will be more hospitable to mandatory greenhouse gas reductions.

Both Obama and McCain have called for capping carbon dioxide and other emissions linked to climate change. President Bush has opposed such measures and said he would have vetoed the Senate bill if he had received it.

The bill would have capped carbon dioxide coming from power plants, refineries and factories, with a target of cutting greenhouse gas emissions by 71 percent by mid-century.

"It's a huge tax increase," argued Republican Senate leader Mitch McConnell of Kentucky, a prominent coal-producing state. He maintained that the proposed system of allowing widespread trading of carbon emissions allowances would produce "the largest restructuring of the American economy since the New Deal."

Supporters of the bill accused Republicans of muddying the water with misinformation.

"There is no tax increase," Sen. Barbara Boxer, D-Calif., one of the bill's chief sponsors said. She said the emissions trading system would provide tax relief to help people pay energy prices. And supporters disputed that it would substantially increase gasoline prices.

Four Democrats joined most Republicans in essentially killing the bill.

Obama and McCain, as well as Sen. Hillary Rodham Clinton, D-N.Y., and Sen. Edward Kennedy, D-Mass., who is recovering from cancer surgery, were absent, although they each sent a letter supporting the bill.