The U.S. House of Representatives is poised to vote on Friday on one of the most significant environmental bills in history -- a sprawling measure that aims to wean industry off of carbon-emitting fuels blamed for global warming.

Democratic leaders were working hard to ensure there were at least 218 votes in the 435-seat House to pass the legislation that is a high priority for President Barack Obama.

It's all hands on deck, one House Democratic aide said of the work lawmakers and the Obama administration were doing to try to ensure passage of the climate change bill.

With House Republicans mostly opposed and warning it would hit recession-weary consumers in their pocketbooks with higher prices for energy and other everyday goods, supporters were attempting to counter those arguments.

It is a jobs bill, House Speaker Nancy Pelosi told reporters on Thursday, referring to the hoped-for growth in green technologies industries.

The American Council for an Energy-Efficient Economy agreed, saying, Savings from reduced energy use will be reinvested locally, creating a multiplier effect that will generate economic activity and jobs.

Both Pelosi and Obama also framed the climate bill as being important to national security by reducing U.S. dependence on foreign oil in favor of developing domestically produced alternative fuels such as wind and solar energy and possibly clean coal.

At the core of the 1,200-page bill is a cap and trade plan designed to reduce emissions of carbon dioxide and other greenhouse gases by 17 percent by 2020 and 83 percent by 2050, from 2005 levels.

CHANGES DESIGNED TO WIN FARM-STATE SUPPORT

Big polluters, such as coal-fired utilities, oil refiners, steel, paper, cement and glass manufacturers and other companies would receive government permits to emit lower amounts of carbon dioxide each year. Companies that end up with more permits than they need could sell them to companies that had not managed to adequately reduce their harmful emissions.

Even if Obama and his fellow Democrats manage to pull off a victory this week, the legislation faces a difficult road in the Senate, where Republicans would have an easier time using procedural hurdles to block the bill.

But passage by the House this year would let Obama attend a December international conference on climate change with a major victory in hand. That conference aims to lay out a global approach to dealing with climate change over the next few decades.

In her quest to find enough votes for the bill, Pelosi has allowed several changes since it was approved in late May by the Energy and Commerce Committee. Those have included new protections for agriculture interests, resulting in House Agriculture Committee Chairman Collin Peterson announcing his support -- a move that could also win the support of about two dozen lawmakers from farm states.

Supporters of the bill received other breaks this week, including the release of a Congressional Budget Office analysis concluding the bill's impact on average households would be around $170 a year in higher costs -- far below the $3,100 or more Republicans have been warning.

A new Washington Post/ABC poll found that three-quarters of the public think the U.S. government should regulate climate-warming greenhouse gases that are being blamed for more severe weather patterns, melting polar ice and threats to animal and plant species.

Even so, Pelosi and Obama were struggling to nail down victory, with the president personally courting a handful of undecided Democrats at the White House.

Some won't be moved, however.

Representative Artur Davis, a Democrat who is considering running for governor of Alabama, told Reuters he would vote against the measure.

The bill has been improved, but this is the wrong time, he said, noting the hard economic times and the lack of commitment from heavy-polluting countries like China and India to significantly reduce their emissions.

(Editing by Stacey Joyce)

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