The US House will likely take a close vote this week on allowing President Barack Obama to speedily conclude a huge Pacific Rim trade accord, Republican congressional leaders signalled Wednesday.

The vote, expected Friday, will be tight by all accounts. While leaders who back the measure including House Speaker John Boehner sense "momentum" in their favor, success is by no means assured.

Obama has earned the support of most Republicans in Congress for his trade push, which could produce a legacy accomplishment for his presidency.

But his Democrats are largely opposed to so-called Trade Promotion Authority.

A 'yes' vote on TPA would not constitute approval of the Pacific trade accord itself, which is still under negotiation with 11 other countries.

It would allow Obama, and his successor, to fast-track international trade accords by allowing Congress an up-or-down vote on the agreements but no ability to amend them.

TPA passed the Senate last month in a victory for Obama, and House leaders said they would hold trade votes as soon as they feel they had sufficient support.

"We're doing really well," House Ways and Means Committee chairman Paul Ryan said as he emerged from a closed-door Republican meeting, adding that leaders have addressed several concerns voiced by skeptics.

"We are in our closing arguments, we're comfortable, and that's why we're proceeding," Ryan said.

House leaders introduced the trade package late Tuesday, a move that a senior Republican aide said gives leaders "flexibility to move on TPA as early as this week."

Progress stalled over how to pay for aid to US workers displaced by globalization, a program known as Trade Adjustment Assistance.

But Boehner said he and top House Democrat Nancy Pelosi worked out a "fix" that would see tighter corporate tax compliance pay for TAA costs instead of drawing them from government-run Medicare health insurance for seniors.

"We're seeing some positive momentum in the right direction," Boehner said.

- Arm-twisting -

Neither Pelosi, a top Obama ally who helped shepherd his landmark Affordable Care Act through Congress in 2010, nor number-two Democrat Steny Hoyer have publicly disclosed how they will vote.

Pelosi has reportedly said TPA would need support from 200 Republicans to cross the finish line, meaning there may be fewer than 20 Democrats willing to support it.

Obama has twisted arms of fence-sitters, including Congressional Black Caucus chairman G.K. Butterfield.

Butterfield told AFP he is leaning against TPA, "but I can be convinced with some more evidence" that the trade deal would add jobs and raise wages in his native North Carolina.

His district suffered under the North American Free Trade Agreement, which critics blame for outsourcing millions of US manufacturing jobs after it came into force in 1994.

"I've got the burden of going home to persuade them that it's different in 2015," Butterfield said.

Anti-TPA Democrats, backed by labor unions, were outspoken in their opposition Wednesday.

Congressman Paul Tonko blasted the trade accord as "NAFTA on steroids."

Democratic head-counters say there are a firm 150 "no" votes among the 188 House Democrats, with more opposition likely.

A few dozen Republicans might vote against it too, leaving little breathing room for TPA passage.

"We're really going to need a very hefty vote on the Republican side," said Gerry Connolly, one of about 19 House Democrats who openly support TPA.

"It's a work in progress," Republican Trent Franks warned.

While Republicans "are collectively very pro-free-trade," Franks said, some in the party "do not trust this president" and may not be willing to give Obama a political victory.