The heads of the Energy Department, Agriculture Department, Interior Department and Environmental Protection Agency told a Senate panel it should pass a bill similar to one the House narrowly cleared late last month. That legislation would impose the first limits on greenhouse gases, eventually leading to an 80 percent reduction by mid-century by putting a price on each ton of climate-altering pollution.

"We will not fully unleash the potential of the clean energy economy unless this committee, and the Senate, put an upper limit on the emissions of heat-trapping gases that are damaging our environment," Interior Secretary Ken Salazar said in prepared testimony. Salazar acknowledged that another Senate panel has already advanced a bill that would boost the amount of energy generated from renewable sources.

Energy Secretary Steven Chu warned that a projected temperature increase would make the world a much different place, and said the only way to avoid that outcome is by enacting legislation to curb emissions, such as carbon dioxide, released by the burning of fossil fuels.

"Denial of the climate change problem will not change our destiny; a comprehensive energy and climate bill that caps and then reduces carbon emissions will," Chu said.

Chu and EPA Administrator Lisa Jackson admitted that reductions in the United States alone will not be enough to avert the worst consequences of global warming. The hope is that the legislation will inspire other countries to also act.

"U.S. action alone will not impact world carbon dioxide levels," Jackson said. "What the U.S. does is important in terms of entering the clean energy race."

The appearance of the three Cabinet secretaries and EPA administrator signals the beginning of the Senate's work on a climate bill. The committee hopes to draft and advance legislation before the August recess, and Senate leaders have said they want to take up the measure later this year, before talks in Copenhagen on a new global treaty to reduce heat-trapping gases.

The House of Representatives narrowly passed its version of the bill 219-212 late last month, after months of negotiations that led to last-minute deals and significant concessions to win the votes of moderate Democrats from industrial and agricultural states concerned about the costs the bill would impose on businesses in their districts.

Further compromises will be needed for the bill to pass the Senate, and the debate launched Tuesday offered some early clues as to where those changes may occur: provisions to boost nuclear energy and to further compensate farmers for projects that would reduce greenhouse gases.

Unlike the House, the Senate has tried and failed to pass legislation to curb the global warming pollution before, a track record Republicans seized on Tuesday.

"You can be sure of this: once the American public realize what this legislation will do to their wallets, they will resoundingly reject it," said Oklahoma Sen. James Inhofe, the panel's top Republican. "Perhaps that explains why we are rushing cap-and-trade through the Senate."

Unlike the House, the Senate has tried and failed to pass legislation to curb the global warming pollution before, a track record Republicans seized on Tuesday.

All four administration officials sought to head off cost concerns, citing analyses by the nonpartisan Congressional Budget Office that estimated the House bill would cost the average household in 2020 less than 50 cents a day.

And that, EPA administrator Lisa Jackson testified, leaves out the benefits of addressing global warming, such as more jobs, less money flowing overseas to oil producers and averting the floods, drought and disease expected to come when the Earth's temperature rises.

"Can anyone honestly say that the head of an American household would not spend a dollar a day to safeguard the well-being of his or her children ... and to create new American jobs that pay well and cannot be outsourced?" she asked.

Sen. James Inhofe, the top Republican on the panel, predicted that Americans would feel the pinch of higher energy prices.

"You can be sure of this: once the American public realize what this legislation will do to their wallets, they will resoundingly reject it," Inhofe said. "Perhaps that explains why we are rushing cap-and-trade through the Senate."