WASHINGTON (Reuters) - Republicans are poised to make big gains in Tuesday’s congressional elections, putting them in position to reverse Democrats’ drive for comprehensive climate change legislation.

President Barack Obama’s Democrats, who largely support legislation requiring the first mandatory cuts in greenhouse gas pollution, currently hold majorities in both chambers of the U.S. Congress.

A Republican takeover of either chamber, or even large gains by the party known for opposing climate change legislation, will make it harder, or impossible, for Obama to win legislation imposing mandatory reductions of greenhouse gas emissions from smokestacks and tailpipes.

That’s especially true if next year’s Senate is populated by more skeptics of human-caused global warming. Democrats in coal-producing states like West Virginia are struggling to win on November 2, partly due to Obama’s climate change proposals.

Even with tough opposition though, Obama still has the power to shape climate change policy. And Republican bills that stray too far from Obama’s energy and environment goals will surely be vetoed.

Here are some possible moves to look out for if Republicans do well in the elections.

EPA REGULATION

Senator John Rockefeller, a Democrat representing West Virginia, is pushing for a vote during the “lame duck” session of Congress planned for mid-November that would suspend Environmental Protection Agency regulation of greenhouse gases, including those emitted from burning coal, for two years. Rockefeller says a two-year pause is needed to give the coal industry time to perfect clean technologies.

Passage would prevent EPA from regulating pollution from large factories and utilities starting in January.

Of 100 senators, 47 voted in June to permanently strip EPA of its power to regulate greenhouse gas emissions.

If a vote isn’t staged during the post-election session this year, Rockefeller is likely to have more Senate colleagues next year, especially Republicans, who would vote with him.

In Rockefeller’s home state, the two candidates running to replace the late Senator Robert Byrd have both campaigned against federal climate legislation.

If the curbs on EPA were to pass Congress, Obama could veto the bill.

HIT EPA WHERE IT HURTS -- ITS WALLET

If Republicans take control of the House of Representatives, they likely would try to stop EPA regulation of carbon by explicitly banning the use of EPA funds to administer such regulations. Annual EPA funding bills that Congress writes would be the avenue. Appropriations bills usually begin moving through the House around March or April.

Republicans could target other pending EPA Clean Air Act rules too, such as one setting limits on smog-producing ozone.

UTILITIES

Renewable Electricity Standard legislation has bipartisan support and is being pushed by Senate Energy and Natural Resources Committee Chairman Jeff Bingaman, a Democrat, as a measure that could demonstrate Congress’ ability to do something for the environment, even with more Republican lawmakers.

The aim is to require big electric utilities to generate 15 percent of their power from renewable sources, such as solar, wind, geothermal and hydroelectric by 2021.

While the legislation is backed by environmentalists, critics say it would barely put a dent in the overall carbon emissions blamed for global warming. Nevertheless, an RES bill could fit nicely into Obama’s latest energy and environment strategy that aims to set new policies in place “in chunks” rather than through comprehensive legislation.

Bingaman, who in September told Reuters that comprehensive climate control legislation is dead for years, could push for an RES vote in the lame duck session if he has enough support.

THE RETURN OF CAP AND TRADE?

If Democrats do better than expected in November, that could revive efforts in Congress for some sort of limited carbon control legislation.

Senators John Kerry, a Democrat, and Joseph Lieberman, an independent who caucuses with Democrats, could bring back their plan to impose a cap on carbon emissions from large electric utilities. Under their bill, pollution permits would be required for each ton of carbon emitted and those permits could be traded on a regulated market, thus setting a price on carbon that could make alternative energy more competitive.

Their hope would be that with the congressional elections behind them, senators would take some tough votes and pass a bill that they could argue would supplant more distasteful EPA regulations.

MORE CHUNKS?

Senate Democratic Leader Harry Reid, in a tough race for re-election in Nevada, could push an energy-environment bill this year or, if he ekes out a win, sometime next year.

He has talked about providing more federal incentives for electric cars, trucks fueled by natural gas, and steps to make buildings more energy efficient.

This, too, would fit well with Obama’s call for “chunks” of bills rather than 1,000-page comprehensive legislation. Tackling global warming bit by bit also would demonstrate to international global warming talks that the United States is still in the climate control game.

OIL DRILLING AND NUCLEAR POWER

A more Republican Congress is certain to see new moves to expand offshore oil drilling, despite the BP disaster in the Gulf of Mexico that resulted in the worst oil spill in U.S. history.

Republicans also would likely try to fight off Democratic attempts to lift oil spill liability limits on companies.

The nuclear power industry also could see a resurgence with a Republican win in November. The industry already has convinced some Democrats to back new federal incentives to increase nuclear generating capacity, which does not contribute to global warming but presents added concerns over waste disposal.

THE POWER OF THE PRESIDENT

No matter how many Republicans populate Congress next year, Obama still has plenty of ways to try to steer the United States away from oil, coal and natural gas.

Some of it is symbolic, such as the installation of solar panels atop the White House after Republican President Ronald Reagan had them removed in the 1980s.

Other steps have more bite: In October, the Interior Department awarded the nation’s first federal licenses for solar plants to operate on public land. Interior Secretary Ken Salazar also signed the first lease for a major offshore wind project, which will be off the coast of Massachusetts.