The U.S. Senate will not vote this week on whether to confirm Federal Reserve Chairman Ben Bernanke for a second four-year term, a Democratic party aide said, raising the risks that time will run out to confirm Bernanke before his current term expires.

Bernanke, whose first term expires on January 31, is still expected to be confirmed, the aide said on Thursday.

If Bernanke isn't confirmed by January 31 it is unclear whether he could continue to run the Fed.

Bernanke is also serving a full 14-year term on the Fed board of governors that ends in January 2020.

Bernanke and the Fed have been under unusually intense criticism for failing to anticipate and prevent the financial meltdown of 2008 and the ensuing massive government bailout.

At least four Senators have holds on Bernanke's confirmation, meaning they are prepared to filibuster, or speak indefinitely on the Senate floor, to prevent a vote from being held on the confirmation. A hold can be overcome via a 60-vote three-fifths majority.

Bernanke has support among both Democrats and Republicans, and most observers believe Senate leadership will be able to muster 60 votes in his favor. Given the holds on Bernanke's nomination, senators will need to file a petition that would set a two-day clock running toward a vote that would enable them to consider the nomination.

If the 60-vote hurdle is then cleared, the Senate would have up to 30 hours of debate before a final confirming vote. Achieving the 60-vote consensus would show that Bernanke has the support needed to win confirmation.

(Writing by Mark Felsenthal; Editing by Leslie Adler)