This time it’s for keeps.

Unlike last year, when the dress-rehearsal debate on global warming sputtered to a halt on the Senate floor without a single amendment vote, both sides are prepping for a fight with full knowledge that the chamber could actually pass a bill limiting greenhouse gas emissions.

Last year, “everyone knew it was just exhibition season,— said Dan Weiss, director of climate strategy for the liberal Center for American Progress. “In 2009, these are the playoffs.—

The biggest boost for cap-and-trade supporters is having the White House in their corner for the first time in eight years. But the support also raises the stakes on key issues that were punted on last year — including backing for coal and nuclear power, and the complicated allocation scheme for carbon credits.

Round Two kicks off later this month in the Senate Environment and Public Works Committee, with an expected markup of the Clean Energy Jobs and American Power Act. The bill, unveiled last month by Sen. John Kerry (D-Mass.) and Environment and Public Works Chairman Barbara Boxer (D-Calif.), aims for greenhouse gas cuts of 20 percent of current levels by 2020, with overall reductions of 80 percent by 2050.

This time around, new faces will play key roles in shepherding the bill to the president’s desk. For starters, Kerry, as the bill’s chief sponsor, is playing a bigger role in marshaling support from Republicans and skeptical Democratic moderates.

“I’m ready to sit down with anybody and talk seriously about how we proceed on it in a serious way,— Kerry said last week.

Less visible is Sen. Joe Lieberman (ID-Conn.), who in previous Congresses led the climate charge with now-retired Sen. John Warner (R-Va.). He’s been relegated to a more peripheral role after Democrats stripped him of his EPW seat for supporting Sen. John McCain (R-Ariz.) in the 2008 White House election.

Warner’s departure also deprives Democrats of the bipartisan veneer they used as a selling point on last session’s bill. So far, Republicans have made clear they don’t want anything to do with the Kerry-Boxer bill, which they are painting as a job killer.

Sen. Lisa Murkowski (Alaska), one of the few Republicans to co-sponsor cap-and-trade legislation last Congress, called the new bill “a massive bill with massive costs.—

Kerry countered that 98 percent of American businesses are exempt from the bill’s mandates, which he maintained would only affect 7,500 major emitters.

“This is a solid first step, without overreach, to deal with 75 percent of America’s greenhouse gases,— he said.

The 900-pound gorillas, both in the Environment committee room and on the Senate floor, will be coal and nuclear power.

Moderate Democrats from states that produce coal, as well as those states who depend on it for electricity, are already signaling they’ll want more support for the fossil fuel. “There’s been an effort to reach out to coal states,— Sen. Tom Carper (D-Del.) said. “We need to do a little bit more.—

Central to those efforts is coal-state Sen. Max Baucus (D-Mont.), who as Finance chairman and a senior member on EPW will have major sway on divvying up the carbon emission allocations created by the cap-and-trade scheme. The Kerry-Boxer bill is currently blank on the issue of allocations, which will be worth billions of dollars. Coal will be treated “fairly— in the bill, Baucus told reporters last week.

Baucus’ panel also has jurisdiction on trade-related aspects of the bill, and observers say he is unlikely to pass on marking up the bill in Finance.

Nuclear supporters also want to see the bill’s limited provisions on the greenhouse-gas-free power source expanded to include more federal loan guarantees and investment in technologies for addressing nuclear waste.

McCain, who previously sponsored cap-and-trade legislation with Lieberman, has made clear the bill’s current treatment of nuclear energy will not earn his support. Without new nuclear plants, “it is difficult to achieve any meaningful reductions in greenhouse gas emissions,— he said last week.

Carper, who has been working with Lieberman and Sen. Lindsey Graham (R-S.C.) on a nuclear power floor amendment, said such provisions could attract some GOP votes. “I think if they see that there’s a robust title for nuclear it will be helpful,— he said.

Passage through the Environment panel is all but assured, and ranking member James Inhofe (R-Okla.) last week said he won’t belabor the debate in committee. However, Inhofe, an avowed global warming skeptic, promised Republicans will offer some amendments “that will be awfully hard for [Democrats] to vote against.—

The bill’s broad jurisdiction also provides an opportunity for two other powerful committee chairmen — newly minted Agriculture, Nutrition and Forestry Chairman Blanche Lincoln (D-Ark.) and Commerce, Science and Transportation Chairman Jay Rockefeller (D-W.Va.) — to take a whack at it. Neither lawmaker is enthused over the bill’s possible impact on their home states.

Senate Democrats can take solace that the House passed similar legislation sponsored by Reps. Henry Waxman (D-Calif.) and Ed Markey (D-Mass.) in June after grappling with the same regional issues. However, that bill was able to advance on a simple-majority vote with limited debate; getting a bill through the Senate may be considerably more cumbersome.

While Democrats and the Obama administration would like to pass the Kerry-Boxer bill before international climate talks in December, the debate is almost certain to slip into 2010, as health care continues to dominate the chamber.

Kerry said the Senate will move “as soon as we can possibly do it,— while continuing to lay the groundwork for eventual passage.

“I think we just need to keep moving, keep working, a very concentrated effort,— he said.