A White House official said on Wednesday that Federal Reserve Vice Chair Janet Yellen is the front-runner to take over the top job at the U.S. central bank when Ben Bernanke steps down, the strongest indication yet of her likely nomination.

The official declined to comment on the timing of any announcement. The Washington Post reported, without attribution, that her identification as leading candidate likely means she will get the nomination, perhaps as soon as next week.

Bernanke's term expires in January and speculation about who will replace him has become pervasive. President Barack Obama's reported favorite for the job, former Treasury Secretary Lawrence Summers, on Sunday withdrew from consideration after widespread criticism of his candidacy from liberal Democrats.

The president has said he was giving thought to Yellen as well as former Fed Vice Chair Donald Kohn, and administration officials had said that once Summers dropped out of contention Yellen became the front-runner.

Separately, Democratic Senator Charles Schumer, who serves on the banking committee, on Wednesday urged President Barack Obama to nominate Federal Reserve Vice Chair Janet Yellen as the next chief of the U.S. central bank.

Yellen, 67, became the U.S. central bank's No. 2 in 2010. Previously she was president of the San Francisco Fed bank, head of the White House Council of Economic Advisers, and a governor on the Fed Board.

The Fed plays a central role in determining the speed of economic growth and keeping inflation under control in the world's largest economy.

It has become much more visible and controversial in the public arena since the 2007-2009 financial crisis, when it helped bail out financial institutions and took unorthodox steps to cushion the blow of the recession and speed up the recovery.