Key lawmakers concerned that President Bush is mishandling the threat of global warming yesterday launched a drive for mandatory limits on carbon dioxide and other heat-trapping gases that many scientists blame for a troubling rise in the Earth's temperature.

Sens. John McCain (R-Ariz.) and Joseph I. Lieberman (D-Conn.) unveiled their plan to require all U.S. power plants and industries to set mandatory targets for the reduction of industrial greenhouse gas emissions at a hearing by the Senate Commerce, Science and Transportation Committee.

Senate Minority Leader Thomas A. Daschle (D-S.D.) and Sen. James M. Jeffords (I-Vt.), meanwhile, touted a new "Global Climate Security Act" to address the problems of climate change and air pollution and promote clean energy. And House Science Committee Chairman Sherwood L. Boehlert (R-N.Y.) and other GOP House moderates are supporting tough measures to combat rising temperatures while voicing impatience with the pace of some of Bush's voluntary initiatives.

"The administration suggests that little or nothing can be done to reduce emissions," Daschle said. "The Senate will lead the United States to address the problem of global warming since the president is unwilling to."

McCain, a maverick Republican who is about to assume the chairmanship of the commerce committee, charged that the administration was using scientific uncertainties about the causes of global warming as an excuse to do nothing. "As I read [the administration's] proposal, it simply doesn't do very much except study the issue another four or five years," he told reporters.

The Bush administration and Sen. James M. Inhofe (R-Okla.), the new chairman of the Environment and Public Works Committee, strongly oppose mandatory limits on greenhouse gases, favoring a voluntary approach instead.

Bush has called for more research into the causes and effects of global warming and a series of economic incentives to encourage utilities and other industrial polluters to gradually reduce the growth of emissions. The administration staged a workshop in Washington last month to highlight many of the remaining uncertainties about climate change science, and James R. Mahoney, assistant secretary of commerce for oceans and atmosphere, announced yesterday that the administration will hold an "Earth Observation Summit" next summer to improve the monitoring of oceans, climate and ecosystems.

White House press secretary Ari Fleischer sought to play down the significance of the rift between McCain and the president over global warming, saying that while the two have worked closely on a number of important matters, "This may be an issue on which, at least at this stage, they don't see eye to eye."

Overall, U.S. greenhouse gas emissions are 11.9 percent above the 1990 level, and the United States remains the largest contributor to the emissions linked to global warming, which experts say will disrupt weather patterns, melt the polar ice caps and harm plants and animals.

This year has been the second-warmest in recorded history. The earth's average temperature during 2002 was 58.35 degrees Fahrenheit, more than one degree warmer than the long-term average of 57.2 degrees, according to climate scientists at the NASA Goddard Institute for Space.

McCain first raised global warming as an issue during the 2000 Republican presidential primaries, and, after losing to Bush, vowed to press for tough standards. He used the first full day of the 108th Congress to highlight his bill and concerns about Bush's handling of the issue, even as the White House and GOP leaders focused on bolstering the economy, health care and looming war in Iraq.

The Senate went on record in 1997 opposing the then-emerging outlines of the Kyoto Protocol on climate change. But last year, the Senate Foreign Relations Committee unanimously voted to encourage Bush to negotiate an international agreement.

Shortly after he took office, Bush disavowed the treaty, saying that it would harm the U.S. economy while exempting major developing countries, including India and China. Even so, much of the industrialized world, including Europe, Japan and Canada, ratified the treaty last year, and Russia is expected to follow suit.

Yesterday, Sen. Conrad Burns (R-Mont.), a conservative who strongly opposed the Kyoto Protocol and mandatory controls on U.S. carbon emissions, told Mahoney: "I do not believe it serves the issue very well or this country very well just to stop talks on the international level on what we can do and should do. I think those talks and that dialogue has to continue."

The McCain-Lieberman proposal would establish a nationwide cap on emissions of carbon dioxide and other heat trapping gases. Under the bill, all major energy, industrial and transportation sources of the six major greenhouse gases would have to limit their emissions to 2000 levels by 2010 and 1990 levels by 2016. The agriculture sector would be exempt.

The bill would establish a trading system that would allow utilities and plants with excessive emissions to buy credits from more efficient companies that have reduced emissions beyond their targets. A similar system has operated for years, under the Clean Air Act, to limit the threat of acid rain.

Sens John McCain (R-Ariz.) left, and Joseph I. Lieberman (D-Conn.) seek cuts in emissions of heat-trapping gases by the years 2010 and 2016.