CNN

Nancy Pelosi is leading a lobbying effort in the House of Representatives to garner the 218 votes necessary to pass key environmental legislation.

WASHINGTON (CNN) – House Democratic leaders are turning up the heat in their efforts to pass a bill aimed at curbing global warming, even enlisting former Vice President Al Gore in the lobbying efforts and getting a public show of support from President Barack Obama at the White House.

Democrats admit that they are shy of the 218 votes needed to pass the climate-change bill scheduled for a vote on Friday, and have furiously been lobbying fence-sitting members.

Gore was scheduled to visit the Capitol on Thursday to personally lobby in favor of the bill, but House Speaker Nancy Pelosi's office called his office Wednesday night to cancel.

"It's a question of what was energy-efficient for the vice president," Pelosi said of the decision to keep Gore in Tennessee. "We were narrowing the list of the undecided and thought that perhaps on another occasion we could call upon his time to come here."

While Gore is not in Washington, his spokeswoman says he is still working the phones and contacting uncertain lawmakers to make the case for passing the Clean Energy and Security Act, which would require a 17 percent emissions reduction from 2005 levels by 2020 and create a "cap-and-trade" system where manufacturers would buy and sell pollution credits.

Pelosi and her leadership team have been entrenched in the lobbying efforts, holding private meetings with moderate Republicans and pigeonholing wavering Democrats on the floor of the House of Representatives in efforts to gain more support for the bill. Democratic aides predict that five to 10 Republicans may end up voting for the legislation.

One Republican that Democrats are hopeful will support the bill is Rep. Mary Bono-Mack, R-California, who voted in favor of the bill when it was in committee, but now has some reservations because of major changes made to the bill in an effort to gain support from conservative Democrats. Bono-Mack remains undecided on how she'll vote but cites the bill's support for the type of burgeoning solar and wind powered industries in her Palm Springs-based district as reasons for her original support.

A spokeswoman for Bono-Mack said the congresswoman is still undecided on district "a leader in research and development of alternative energy."

Despite the possibility that a handful of Republicans will vote for the climate change bill, party leaders continue to pound their message that a new set of environmental regulations will overtax Americans and eliminate jobs.

"We are going to shift jobs overseas. It's what's fundamentally wrong with this," said House Minority Leader John Boehner, R-Ohio. "It's not just about higher cost. This really is about shipping millions of American jobs overseas."

A recent report by the Congressional Budget Office (CBO) estimates that the annual economy-wide cost of the cap-and-trade program in 2020 would be $22 billion - or about $175 per household.

Democratic leaders say they hope ongoing negotiations with undecided lawmakers will help persuade them to support the bill when it eventually comes to a vote.

Rep. Diana DiGette, D-Colorado, who counts votes as the House Democrats' chief deputy whip, told reporters that the lobbying effort is still underway and that the bill's ultimate fate remains unclear.

"I'm not confident about anything. But we're closing in on it," she said.