Democratic House Majority Leader Steny Hoyer predicted Friday that his party would have the 218 votes needed to ensure passage of historic legislation to battle global warming.

"We'll have the 218 votes," Hoyer told AFP in a telephone interview hours before lawmakers were expected to take up the sweeping bill between 3:00 pm and 4:00 pm (1900 GMT and 2000 GMT).

US President Barack Obama and top aides were still reaching out to wavering lawmakers, while Republicans mounted their own campaign to defeat the massive plan, which would create a "cap-and-trade" system to curb greenhouse gases.

"We expect that we will have the number of votes to pass the bill," Hoyer said. "We worked late yesterday and we're still working this morning. This is a very big piece of legislation and complex. Members are giving (it) a lot of thought."

Obama, White House chief of staff Rahm Emanuel, and other advisors were reaching out to lawmakers by telephone in a bid to corral the votes needed for passage, a White House source told AFP.

"The president feels very strong about this bill. It's one of his major priorities and he is also talking to members and urging them to support this legislation," Hoyer said.

The White House source cautiously declined to speculate on the vote count, or to say whether the White House believed the legislation would pass, while Republican sources shied from discussing their own vote count.

Republicans hoped to hold together and peel off a handful of swing-vote Democrats to defeat the legislation, which Obama has made a key priority ahead of December global climate change talks in Copenhagen.

The Senate will likely not act before mid-September, when leaders of key committees are due to make their proposals public, launching what could be a months-long process to get the measure through the Senate, reconcile any differences with the House version and pass a final bill.

The House's "American Clean Energy and Security Act" aims to reduce greenhouse gas emissions 17 percent from 2005 levels by 2020, while creating "green" jobs.

The 1,200-page bill, the fruit of months of tough negotiations, would create a "cap-and-trade" system limiting overall pollution from large industrial sources and then allocating and selling pollution permits.