A group of major corporations yesterday launched the nation's first trading program to reduce releases of carbon dioxide and other "greenhouse gases" through trades of credits earned by firms that exceed emission-reduction goals.

The creation of the Chicago Climate Exchange marks an expansion of market-based steps to cut U.S. emissions linked to global warming. Such voluntary strategies have become a sharp fault line between President Bush and Democratic congressional leaders and some key Republican lawmakers as well.

The Bush administration opposes mandatory reductions in carbon dioxide and other greenhouse gases. Instead, the president has called for more research on global warming and new economic incentives to encourage utilities and manufacturers to gradually reduce the growth of emissions.

Environmental Protection Agency Administrator Christine Todd Whitman said last week that the president intends to press for passage this year of his "Clear Skies" legislation, which would cut health-threatening power-plant emissions of sulfur dioxide, nitrogen oxide and mercury but would not address carbon dioxide.

But administration opponents are stepping up demands for a more forceful solution, particularly on carbon dioxide and other greenhouse gases that trap heat within the earth's atmosphere.

A proposal this month by Sens. Joseph I. Lieberman (D-Conn.) and John McCain (R-Ariz.) would require U.S. power plants and industries to set targets for limiting greenhouse emissions.

Yesterday, Senate Democrats Hillary Rodham Clinton (N.Y.) and Barbara Boxer (Calif.) and independent James M. Jeffords (Vt.) -- all key players in the clean-air debate -- said they were unwilling to compromise with the administration on new clean-air legislation unless it includes cuts in carbon dioxide.

"We have been very clear in the Environment and Public Works Committee that we want to pass legislation that takes us forward, not backwards," Clinton said during a news conference called to criticize Bush's environmental record. Lieberman said yesterday that the pilot emissions-trading project -- coupled with mandatory emission reductions -- would be an effective combination. "The Chicago Climate Exchange is precisely the kind of market mechanism that our bill contemplates, and that will thrive in the new environment that our bill, if passed, creates."

Britain and Denmark have trading programs for greenhouse gases. A mandatory U.S. trading program has contributed to large-scale reductions in sulfur dioxide, a source of acid-rain pollution, experts say.

A critical policy issue is whether trading will work without enforceable targets, said W. David Montgomery, vice president of Charles River Associates, a consulting firm. Some exchange members said yesterday that they hoped to prove that mandatory goals aren't necessary.

Patterned after commodity exchanges, the Climate Exchange intends to create verifiable ways of measuring reductions of greenhouse-gas emissions. Some measures will be direct, such as changes to more efficient industrial processes. Others will involve indirect emissions "offsets" through increased plantings of forests or farm products that absorb carbon dioxide, or steps to control gas releases from landfills, said Richard L. Sandor, the exchange's chairman and chief executive.

The 14 initial exchange members include DuPont Co., Ford Motor Co., International Paper Co., Motorola Inc., American Electric Power and the City of Chicago. Discussions are underway with more than 50 other potential members, Sandor said. However some original business participants in the project did not sign up yesterday.

Each exchange member agrees to reduce average greenhouse-gas levels from 1998 to 2001 by 4 percent over the next four years.

Sandor said the exchange will have to persuade traders -- and skeptics -- that the claims of emissions reductions are valid. It is working with scientific groups on verification and has hired NASD, a securities industry self-regulatory body, to monitor compliance by exchange members.

Companies that exceed reduction goals could sell excess reductions to other members that were falling behind their targets. The price would be set by bids on the exchange. Members that failed to meet the 4 percent target would be disciplined at that time by the exchange, Sandor added. "Would they face sanctions?" he said. "Absolutely."

EPA chief Christine Todd Whitman has said President Bush will push his "Clear Skies" plan, which does not address carbon-dioxide emissions.