WASHINGTON (Reuters) - The U.S. Senate on Monday narrowly confirmed Stephen Miran to the Federal Reserve's Board of Governors, expanding President Donald Trump's influence over the world's most important central bank and handing his top economic adviser one of 12 interest-rate-setting votes on the eve of a key policy meeting.

The 48-47, largely party-line vote in the Republican-controlled Senate on Monday marked the final step of a swift process that began in August when Adriana Kugler resigned unexpectedly as a Fed governor. That created an opening on the seven-member Fed board for Trump to fill with someone more amenable to lowering interest rates, as the president has demanded for all year.

Senator Lisa Murkowski of Alaska was the lone vote against Miran from Republicans.

It typically takes months for a Fed governor nominee to be confirmed by the Senate; in Miran's case it took fewer than six weeks.

Pending the completion of paperwork and his swearing-in, Miran will take part in the U.S. central bank's two-day policy meeting that starts on Tuesday. Fed policymakers are expected to approve a quarter-percentage-point rate cut to support a weakening labor market at the end of the meeting on Wednesday. 

Analysts anticipate that Miran will dissent on the policy decision in favor of a bigger rate cut, though not necessarily the several-percentage-point reduction that Trump has demanded.

As the head of the White House's Council of Economic Advisers, Miran has repeatedly said he believes the Republican president's hefty import tariffs won't cause inflation and that the president's other policies, including his immigration crackdown, will ease broad price pressures by reducing demand for housing.

As the newest Fed board member, Miran would have responsibilities that extend beyond voting on interest rates; governors typically serve on several committees with remits including U.S. financial regulation and supervision, community banking, and staffing and budget decisions for the U.S. central bank's system as well as its 12 regional banks. 

Miran will retain his White House job but go on unpaid leave while he serves at the Fed for a term that expires January 31, although he could stay on indefinitely if a successor for his Fed seat has not yet been picked and confirmed.

Democrats say the arrangement makes him a Trump "puppet," a charge that Miran denies.

Two other Fed governors appointed by Trump in his first term - Michelle Bowman and Christopher Waller - dissented during the July 29-30 meeting in favor of easier policy, and analysts say weaker-than-expected labor market data since that time could move them to dissent again in September in favor of a larger rate reduction than the quarter of a percentage point broadly priced in by financial markets.

A triple dissent by Fed governors has not occurred since 1988, early in former Fed Chair Alan Greenspan's term.

(Reporting by Ann Saphir; Editing by Dan Burns, Paul Simao and Lincoln Feast.)