(Adds rejection of currency rules mandating sanctions)
By Richard Cowan and Jason Lange
WASHINGTON, May 22 (Reuters) - The U.S. Senate on Friday was poised to approve the "fast-track" authority that President Barack Obama says he needs to complete a 12-nation Pacific Rim trade deal central to projecting American influence in Asia.
The Republican-controlled Senate narrowly rejected a push by some lawmakers to include rules to punish currency manipulators, a measure the Obama administration worked to defeat. An alternative amendment, one that opponents said lacks enforcement, was approved.
Even if a six-year "trade promotion authority" (TPA) bill, as fast-track is known, passes as expected, it faces a difficult future in the House of Representatives, where supporters must overcome opposition from most Democrats and some conservative Republicans.
Under fast-track, lawmakers would give Obama and his successor in 2017 the power to negotiate trade deals with foreign governments knowing that Congress could offer input but only approve or disapprove the deals and not amend them.
Most immediately, it is the tool Obama needs to complete the Trans-Pacific Partnership (TPP) trade agreement this year, an economic alliance that would encompass 40 percent of the world's economies in countries ranging from Japan to Chile.
Earlier on Friday, Japanese Economy Minister Akira Amari said ministerial meetings on TPP are unlikely until Congress approves fast-track authority for Obama.
But the deep divisions within the U.S. Congress were on display on Friday.
"We all know that by passing this legislation, we can show we're serious about advancing new opportunities for bigger American paychecks, better American jobs, and a stronger American economy," Senate Majority Leader Mitch McConnell, a Republican, said, urging his 99 Senate colleagues to vote for the bill.
Senate Democratic leader Harry Reid dismissed the emerging TPP as just another trade deal, like past ones, that does little more than help rich, multinational corporations while jeopardizing American jobs.
"This trade bill is another example of how we have ignored in this Congress working men and women in this country," Reid said.
Assuming Senate passage on Friday, just before the start of a 10-day Memorial Day holiday congressional recess, the House likely would take it up in June.
House Speaker John Boehner and Obama will have to use all of their powers of persuasion to overcome spirited opposition from U.S. labor and environmental groups, as well as some conservative lawmakers and lobbying groups that do not want to give Obama any new powers. (Additional reporting by Krista Hughes; Editing by Steve Orlofsky and Leslie Adler)