The Bush administration has received some of its most strident criticism on environmental issues, most recently for its plan to seek voluntary and not mandatory cuts in U.S. greenhouse gas emissions. Its withdrawal last year from the Kyoto climate treaty prompted an international outcry.

Global warming is thought to be caused by the atmospheric buildup of heat-trapping greenhouse gases such as carbon dioxide from the burning of fossil fuels.

The 3-1/2-page letter applauded the U.S. State Department's report issued in May that cited the threat to ecosystems and coastlines from rising global temperatures and sea levels, but criticized the administration for not acting on it.

"While we are certainly heartened that the United States has now officially recognized the existence and scope of the climate change problem, the administration has yet to propose a credible plan that is consistent with the dire findings and conclusions being reported," the letter said.

"In light of the (State Department) Report's findings, however, we urge you now to rethink the administration's policy response to the problem," the letter said.

An administration suggestion to increase the use of air conditioning to combat higher temperatures would only add to the emissions problem by increasing demand for power, it said.

Some individual states were moving "to fill the void left by federal inaction on this issue" by instituting carbon dioxide reductions by power plants or by vehicles, creating potential regulatory conflicts and uncertainty for business. The global nature of climate change lent itself to regulation at the national level, the letter said.

The attorneys general suggested creation of a market-based "cap" on greenhouse gases, a system used successfully on a smaller scale to curtail emissions whereby power plants buy or sell a shrinking pie of rights to emit certain pollutants.

Signatories to the letter were Attorneys General Thomas Reilly of Massachusetts, Bill Lockyer of California, Bruce Botelho of Alaska, Richard Blumenthal of Connecticut, Steven Rowe of Maine, Joseph Curran of Maryland, Philip McLaughlin of New Hampshire, Eliot Spitzer of New York, Sheldon Whitehouse of Rhode Island, William Sorrell of Vermont, and independent David Samson of New Jersey.