Kent Garber

For several months now, the Environmental Protection Agency has been making steady progress writing rules to regulate greenhouse gas emissions. But Alaska Sen. Lisa Murkowski, a Republican, wants to hit the brakes. This Thursday, she's scheduled a vote in the Senate on a resolution that would essentially strip the EPA of its authority to regulate carbon dioxide and other gases linked to climate change.

So far, Murkowski has rallied support from at least 40 senators, ranging from those with doubts about the science of global warming to those who want Congress to set the rules for such key regulatory decisions. "If Murkowski has her way, every EPA effort to limit greenhouse gases would be blocked," says Frank O'Donnell, president of the nonprofit Clean Air Watch. "It would include cars, trucks, power plants, and everything else."

To be sure, even if Murkowski succeeds -- which observers say is a long shot -- the likelihood that Congress will stop the EPA from moving ahead is slim. The House would have to follow suit, and there's nothing to suggest it has any interest in doing so. And, of course, President Obama could veto it.

But perhaps more important is what the vote says about the status of the country's energy policies. For more than a year, the Senate has talked about passing an energy and climate bill like the one the House passed last summer. Among other things, it would give Congress the power to regulate greenhouse gases. But thanks to the contentious healthcare and financial reform debates, the Senate has put off debate. Meanwhile, the EPA -- after its "endangerment finding" last year that greenhouse gases constitute a public health threat -- is legally required to regulate them in the absence of action by Congress. It has written emissions rules for big polluters like factories and refiners that could take effect as early as next year.

That pressing timeline has both sides looking for political opportunities. Some of Murkowski's supporters see her resolution as a way of showing opposition to what they consider a big-government move by EPA. And they're hopeful that if Murkowski can get close to 50 votes, it might indicate that support is waning for legislation on climate change. Many Democrats, on the other hand, hope a failed vote will show that there is support for a climate bill and believe that EPA's actions will continue to put pressure on Congress to act.

Not surprisingly, the upcoming vote has prompted both sides to action. On Tuesday, the National Association of Manufacturers came out in support of Murkowski. A pro-coal group, America's Power Army, has been calling voters, urging them to press their senators to support the resolution. Environmentalists, for their part, are buying up radio spots in Indiana, Virginia, and other swing states, warning against her measure, and EPA chief Lisa Jackson gave a speech this week defending the agency's moves and warning about what would happen if Murkowski's text became law.

The car industry has weighed in, too, siding with the administration.

A year ago, automakers and the White House agreed on stricter fuel-economy and vehicle-emissions standards. The car companies were happy since the accord gave them a single national standard rather than more than a dozen state standards. But the legal basis for the national standards is the EPA's endangerment finding.

If you take that away, as the Murkowski measure effectively would do, "it would create a regulatory nightmare for manufacturers," says Charlie Territo of the Alliance of Automobile Manufacturers, the auto industry's top advocacy group. It's an argument that's giving many Democrats cover as they try to push back against Murkowski's move.