WASHINGTON (REUTERS) - President Barack Obama's quest for "fast-track" negotiating authority on a Pacific Rim trade deal passed its first test in the US House of Representatives on Thursday, with another day of voting to come on a contentious package of bills.

By a vote of 397-32, the House approved a measure authorising funds to help workers who lose their jobs as a result of trade deals, without cutting Medicare health benefits for the elderly to pay for it, as the Senate had proposed.

The vote moved lawmakers closer to dealing with the core issue before them, the fast-track bill expected to come to a vote on Friday. Already approved by the Senate, fast-track is needed, Obama says, to help him promptly conclude a 12-nation Trans-Pacific Partnership (TPP) trade deal.

In an unusual coalition, the Democratic president and House Republican leaders are allied in supporting fast-track. Most Democrats and some Republicans oppose it. The authority would strip Congress of the ability to make changes to a trade deal, but allow it to hold a yes-or-no vote on one.

If fast-track is approved, it would go to Obama's desk to be signed into law, giving him more sway in negotiating the TPP and reassuring Japan, the second-largest economy involved. Japanese officials have said fast-track approval is needed for the pact, which would encompass 40 per cent of the global economy.

Republican House Speaker John Boehner declined to guarantee victory on fast-track. "We're working hard to get there," he told reporters at a press conference.

He said he had worked to address concerns of lawmakers from both parties. He said if the TPP founders, leaving the United States on the trade sidelines, "our allies will gravitate back towards China, away from us and away from our workers."

In a sign of the importance of the issue to Obama, the White House dispatched Treasury Secretary Jack Lew, Labour Secretary Thomas Perez and White House Chief of Staff Denis McDonough to the Capitol to advocate for fast-track with House Democrats.

After administration officials left a closed-door meeting with House Democrats, Richard Trumka, president of the AFL-CIO labour federation and an opponent of fast-track, then spoke.

Labour organisations oppose fast-track, saying it does not give Congress adequate oversight of trade deals that they fear will result in American job losses.

Failure to pass fast-track would seriously hamper Obama's drive to finish the TPP, a centerpiece of his goal to improve US ties with Asia, this year.

The House was expected to debate later on Thursday the procedures it will use for considering fast-track and a related customs enforcement bill on Friday.

On the funding authorisation for worker assistance just approved by the House, the Senate was also expected to promptly approve it, sending it to Obama for enacting into law.

The worker aid is important to Democrats, some of whom will be needed in voting on Friday on the fast-track legislation itself.

Also on Friday, the House will take another vote on trade adjustment assistance, which, like fast-track, could be much closer than Thursday's vote.