By Deborah Zabarenko, Environment Correspondent
WASHINGTON (Reuters) - The U.S. Senate began debate on Tuesday on comprehensive climate change legislation, with opponents citing its cost to the economy and supporters urging action to make the United States an international leader.
The measure, known as the Lieberman-Warner Climate Security Act, is the first to reach the Senate floor, and its future is murky. Even if Congress approves it, President George W. Bush is expected to veto it.
Still, supporters said the bill would lay down a marker for future action, especially by the next U.S. president.
"This bill will signal that the United States, after a long period of doing nothing, is prepared to stand up tall and to lead," Sen. Dianne Feinstein, a California Democrat, told the session.
Bush has consistently opposed any economy-wide program to curb the carbon dioxide emissions that spur climate change, arguing that this would hurt the U.S. economy.
Sen. Bob Corker, a Tennessee Republican, said he accepted the science that supports limiting carbon emissions but said the bill "squanders ... opportunity" in favor of "old-time politics" catering to special interests and raising government spending.
Corker also indicated he wanted to see more support for nuclear power, which does not emit greenhouse gases but does pose a problem about disposal of spent nuclear fuel.
The legislation being debated sets up a cap-and-trade system for carbon emissions and could cut total U.S. global warming emissions by 66 percent by 2050, its proponents say. U.S. greenhouse gas emissions would drop by about 2 percent per year between 2012 and 2050, based on 2005 emission levels, under the measure.
The bill would cap carbon emissions from 86 percent of U.S. facilities, and emissions from those would be 19 percent below current levels by 2020 and 71 percent below current levels by 2050, according to a summary of the bill's details released by the Senate Environment and Public Works Committee.
Carbon dioxide, which contributes to the climate-warming greenhouse effect, is emitted by fossil-fueled vehicles, coal-fired power plants and natural sources, including human breath.
All three major presidential candidates -- Democrats Hillary Clinton and Barack Obama and Republican John McCain -- are senators who can vote on this bill, and all three support taking action to stem the impact of climate change.
None of the three candidates was present for Tuesday's general debate, which precedes substantive discussion of the bill, which could take two weeks.
(Editing by Cynthia Osterman)