WASHINGTON -- A vote scheduled for today targeting the Environmental Protection Agency could be a barometer for how the Senate will approach climate legislation this year -- and whether it does at all.

The EPA in December issued a controversial "endangerment finding" on carbon emissions, essentially declaring that they are a threat to human health because they cause global warming. Though the agency has not announced any plans to impose regulations beyond motor vehicles, the finding opens the door for it to do so for any emitters under the Clean Air Act in lieu of congressional climate legislation.

Sen. Lisa Murkowski, R-Alaska, responded by introducing a resolution to block the EPA from regulating carbon emissions, claiming that the Obama administration is trying to bypass Congress on the issue and impose its preferred "cap-and-trade" policies by itself.

Both of Pennsylvania's senators, Democrats Arlen Specter and Bob Casey, said they will vote against the measure -- but a handful of centrist Democrats, including Jay Rockefeller of West Virginia, have expressed support, along with most of the Republican caucus. The amendment needs 51 votes to pass.

"It's going to be a close vote, for sure," said Adam Garber, an organizer for PennEnvironment who has been lobbying the offices of Mr. Casey and Mr. Specter.

Environmental advocates had been concerned that Mr. Specter, who vocally opposed Ms. Murkowski's amendment when it was introduced, could reverse course since he lost the Democratic primary race last month. But spokeswoman Kate Kelly said Mr. Specter still plans to vote against the bill.

Mr. Casey and Sen. Tom Carper, D-Del., could offer a compromise if they think one is needed to shoot down the Murkowski amendment. Mr. Casey said Wednesday that if a substitute bill is needed to lock down the votes, he and Mr. Carper would propose a measure to prevent EPA from regulating farms and smaller emitters and perhaps delay its action.

Ms. Murkowski's plan, he said, is too broad.

"EPA has a role to play in this, and we shouldn't knock their legs out from under them," Mr. Casey said.

The manufacturing community has lined up against the EPA and in favor of Ms. Murkowski.

"What [President Barack] Obama's EPA is trying to do is going to be, not only really bad for business and for the economy, but it's not scientifically sound -- it's not necessary," said David Taylor, president of the Pennsylvania Manufacturers Association. "This will have a disproportionate impact on Pennsylvania because Pennsylvania is a carbon-intensive state, so we are watching this."

The National Association of Manufacturers was one of 24 business trade associations that joined in a letter to all 100 senators urging a yes vote to oppose the "de facto new national energy policy via regulation." Also signing the letter were the powerful U.S. Chamber of Commerce, the American Iron and Steel Institute and the American Petroleum Institute.

Despite the lobbying frenzy, the bill has a minuscule chance of becoming law, as Mr. Obama has vowed a veto. But today's vote has symbolic value to see where votes might fall on a climate bill -- which Mr. Obama has vowed to press this year, with the Gulf of Mexico oil spill as a backdrop.

"It will provide insight, but not clairvoyance," Mr. Casey said of the link between the two initiatives.

Sens. John Kerry, D-Mass., and Joe Lieberman, I-Conn., introduced a climate bill last month that would set aggressive emissions reduction targets and create a cap-and-trade system in which a price is set to emit carbon above a certain level and the right to do so is traded in a newly created market for big polluters.

For months the two senators negotiated with a lone Republican, Lindsey Graham of South Carolina, but talks fell apart. On Wednesday Mr. Graham endorsed a new energy plan by Sen. Richard Lugar, R-Ind., that emphasized efficiency standards but did not include cap-and-trade.

At least one Republican vote is needed for the 59-member Democratic caucus to get legislation through the Senate.

Washington correspondent Daniel Malloy writes the "Pittsburgh On The Potomac" blog exclusively at PG+, a members-only web site of the Pittsburgh Post-Gazette. Our introduction to PG+ gives you all the details.