WASHINGTON - House Republican leaders set a showdown vote for Friday on legislation that would give fast-track trade promotion authority to President Barack Obama.

"The vote is Friday," said Representative Tim Walberg, a Michigan Republican, as he was left a closed-door meeting among Republicans Wednesday in Washington. He said Speaker John Boehner and other House leaders told rank-and-file Republicans of the plan during the meeting.

The fast-track measure, passed in May by the Senate, would let Obama submit trade agreements to Congress for an expedited, up-or-down vote without amendments. The president has said he wants to complete a 12-nation Trans-Pacific Partnership and send it for approval under that procedure.

Whether there is enough support to pass the bill has been the running question and the vote is expected to be tight. The vote will represent a test for Representative Steve Scalise of Louisiana, the top Republican whip counter, and his lieutenants.

Republicans control the House, 246-188, meaning that if all members vote, support from 218 lawmakers is needed to pass a bill.

Most Republicans are backing Obama, who contends the trade measure would help US workers and set rules for the global economy. Many Democrats remain stung by the 1994 North American Free Trade Agreement, which labour unions blame for a decline in US manufacturing jobs.

Two House aides said, at the end of May during a congressional recess, that informal vote counts showed more than 200 Republicans supporting the measure and about 25 House Democrats prepared to vote yes - enough for a clear majority. The aides had sought anonymity to discuss the count.

Representative Nancy Pelosi of California, the Democratic leader, on Tuesday said the issue of how to fund Trade Adjustment Assistance, a programme designed to aid workers displaced as a result of trade deals, was still unresolved.

House leaders have been wrangling over how guarantee its funding, about US$700 million (S$939 million). The current plan would reduce funding for Medicare, a step that has drawn strong opposition from a range of Democratic-leaning groups.

"I'm concerned right now about TAA," Pelosi told reporters following a meeting with Boehner.