(Adds details on House vote, comments on immigration and currency)
WASHINGTON, April 30 (Reuters) - A key U.S. lawmaker said on Thursday he is optimistic Congress will pass legislation key to a Pacific trade pact and said he is open to considering stronger rules against currency manipulation in a separate bill.
The Republican chairman of the House of Representatives Ways and Means Committee, Paul Ryan, said he thought Republicans were in a "very good place" on a bill granting the White House authority to seal trade deals and submit them to Congress for a yes-or-no vote, without amendments.
Support from Democrats would be needed to pass the bill, but he did not think lawmakers would allow a proposal put forward by a Democratic president to fail.
"I feel reasonably optimistic," Ryan said at a breakfast hosted by the Christian Science Monitor. "I believe we will get there, but trade is always difficult."
The bill is seen as key to encouraging trading partners negotiating the 12-nation Trans-Pacific Partnership to make final offers, with certainty that the deal will not be picked apart in Congress later.
The pact is a key part of President Barack Obama's diplomatic pivot to Asia and has been portrayed by the administration as a counter to China's rising economic and diplomatic clout.
The Wisconsin lawmaker said he opposed changes approved by a Senate panel to a related trade bill which would allow import duties to be imposed on goods from trading partners deemed to be manipulating their currencies.
But he was open to considering another amendment in that bill, supported by the administration, which would allow currency-cheating nations to be blocked from future trade deals and boost scrutiny of currency policies.
Treasury argues that currency rules may backfire against central bank stimulus, including from the U.S. Federal Reserve.
No date has been set yet for a House vote. Republicans have 244 seats in the 435-member House, although some of their number oppose fast track. A Democratic aide said 12-20 Democrats were ready to support the bill.
"Those numbers are a floor, not a ceiling. There are plenty of uncommitted Democrats out there left to get," the aide said.
Ryan said reported estimates that more than 75 Republicans might oppose the bill were not realistic and said a concern raised by some conservatives that fast track could open the door to easier U.S. immigration policies was an "urban legend." (Reporting by Krista Hughes; Editing by Bill Trott and Andrew Hay)