President Obama, Democratic leaders in Congress, and environmentalists all want to get rolling on a national renewable electricity standard (RES), which would require utilities to increase the amount of power they generate from solar, wind, and other renewable sources. But getting an RES through Congress won’t be a cakewalk.

In the House, the chances are good. The House easily passed an RES in 2007, which would have required 15 percent of electricity in the U.S. to come from renewables by 2020. It’s likely to act soon on a new, tougher version — probably the RES bill from Ed Markey (D-Mass.) and Todd Platts (R-Pa.), which calls for 25 percent renewables by 2025.

But the Senate is another story. Sen. Jeff Bingaman (D-N.M.), chair of the Energy and Natural Resources Committee, tried to get an RES passed in 2007 as part of a larger energy bill, but the bill failed to muster enough votes until the provision was dropped. Bingaman is planning to introduce a new RES measure within the next month or so. It’s weaker than the Markey/Platts bill, with a top target of 20 percent renewables by 2021, and a provision that would allow a quarter of that target to be met through energy efficiency.

But even though Bingaman’s bill is relatively moderate, its chances in the Senate this year are unclear. Greenwire‘s Ben Geman has an excellent breakdown on who and what might stand in the way of an RES in the Senate, a must-read for political junkies.

For everyone else, here’s the gist: Essentially, Democrats have 59 votes in the Senate (if Al Franken ever gets seated … ). The bill would need 60 votes to get cloture and surmount a filibuster threat. Republicans like Olympia Snowe and Susan Collins of Maine, Arlen Specter of Pennsylvania, and Chuck Grassley of Iowa could swing in favor of the bill. But Democrats like Evan Bayh of Indiana, Mary Landrieu of Louisiana, and Blanche Lincoln of Arkansas have expressed misgivings about an RES. These senators are the ones to watch.

Landrieu could probably be won over with the promise that nuclear power would be counted toward the renewable goal, but Bingaman and other RES backers don’t like that idea. In a briefing with reporters on Thursday morning, Bingaman argued, “The size [of nuclear plants] are such that it takes away any real impetus for development of renewable energy.” Other fence-sitters might also be won over by various tweaks to the bill or a broadening of what is meant by “renewable.” Bingaman said he has not yet settled on the “right definition” of renewables for his bill.

House Speaker Nancy Pelosi (D-Calif.) has said she intends to wrap the RES into a broad bill that addresses energy issues and sets up a cap-and-trade program to tackle climate change. Bingaman said on Thursday that he wants to keep energy legislation separate from a climate bill in the Senate, but that puts him at odds with Senate Majority Leader Harry Reid (D-Nev.), who now says he wants to move energy and climate measures in one bill.

Bingaman said an RES and other energy measures would be better off on their own. “My view has been that we have reasonable consensus on quite a few things we can do to meet our energy challenge,” said Bingaman. “I think that it’s worthwhile to get that done separate from a cap-and-trade system. I’d hate to see that held hostage while we wait to pass cap-and-trade.” He added that cap-and-trade is “not ready for prime time.”

Bingaman will be unveiling additional components of his energy legislation over the next few weeks. Stay tuned.