WASHINGTON (CNN) -- The Senate on Monday voted to debate a Democratic-backed bill to dramatically cut harmful greenhouse gas emissions by 2050.
But Republicans say they will later block the bill's passage because they are concerned it would increase energy costs and damage the U.S. economy, according to lawmakers and aides from both parties.
The White House opposes the bill, which is designed to reduce the amount of carbon dioxide and other greenhouse gases released into the atmosphere by 2 percent a year starting in 2012 until emissions are reduced by 66 percent in 2050.
Speaking at a White House event Monday, President Bush warned the additional costs associated with the bill, which he estimated at $6 trillion, would be too much of a burden on the American economy.
"There is a much better way to address the environment than imposing these costs on job creators," Bush said. "We'll work with the Congress, but the idea of a huge spending bill fueled by tax increases isn't the right way to proceed."
The bill uses a "cap-and-trade" system wherein the government would cap the amount of pollution a company is allowed to emit -- which would be lowered each year -- but would also give companies some flexibility by allowing them to buy pollution credits from companies whose emissions fall below their caps.
Under the bill, the government would auction off the credits and use some of the proceeds to help consumers who are expected get hit by higher energy costs.
"These higher temperatures are going to cause terrible problems all over the world -- more extreme weather events, vectors that we haven't seen before. The military people say that it's going to be a cause of wars in the future. So we must act," she said in an interview with CNN.
But many Republicans say the bill's costs are too high.
"The impact of this climate tax is too great to bear for Kentuckians and for the rest of the country," Sen. Mitch McConnell of Kentucky, the Senate minority leader, said Monday as the debate began.
"At a time when Americans are struggling to pay their bills and when the price of gas seems to be rising higher and higher every day, [the Democratic] majority is showing itself to be laughably out of touch by moving to a bill that would raise the price of gas even higher."
But the top Democrat in the Senate said the United States "is obligated to lead, not to follow, on this most important issue of our time and perhaps of all time" and that doing nothing would be even more costly.
"President Bush says 'let's bide our time until 2025,' " Senate Majority Leader Harry Reid said Monday. "Is it really cheaper to do nothing? Of course not. It's just the opposite. The longer we wait, the more it will cost to solve this very difficult problem."
Regardless of their opposition, GOP senators will vote to begin the debate because "Republicans need to explain the problems with this bill," said Don Stewart, a spokesman for McConnell. But Republicans will ultimately block the bill before it faces a final vote, he said.
The bill was written by Sen. Joe Lieberman, an independent from Connecticut, and Sen. John Warner, a Republican from Virginia.
Interest groups such as the Club for Growth, which opposes the bill, and the Environmental Defense Fund, which supports it, have lobbied furiously on the issue. Both are running TV ads in multiple states targeting senators up for re-election as well as those in states with industries that could be affected by the bill.
But Sen. John McCain of Arizona, the presumed Republican presidential nominee, who many thought would vote for it because he has supported the idea of "cap and trade," appeared poised to vote against the measure because, he says, it doesn't do enough to boost the use of nuclear power.
At a news conference Friday, McCain called nuclear power "such a vital aspect of any real meaningful action to reduce greenhouse gas emissions."
If McCain opposes the legislation, it will be a relief to some Republican senators who think the Democrats' scheduled action on it will highlight differences between rank-and-file Republicans and their expected presidential standard bearer, according to a Senate Republican leadership aide.
Either way, supporters of the measure think they are laying important groundwork for a bill that could pass in the next Congress and be signed into law by any one of the three presidential contenders.
CNN's Ted Barrett contributed to this report.