Washington — President Barack Obama on Wednesday will nominate Federal Reserve Vice Chair Janet Yellen to lead the U.S. central bank, officials said, selecting a renowned economist focused on combating unemployment for one of the most powerful positions in the world.

Yellen would become the first female chief of any major central bank. As Fed chairman, she would have vast power over the economy, and her record suggests that she would use it to continue for as long as possible a Fed stimulus program aimed at boosting growth. She would also be the top regulator of the nation's financial system, an area in which less is known about her views.

Yellen, 67, who was chairman of the Council of Economic Advisers in the Clinton administration, would become the first Democrat to lead the Fed since Paul Volcker stepped down in 1987.

"Markets will be comfortable with a familiar face," said Michael Feroli, chief U.S. economist at JPMorgan Chase.

"I think she will be pretty aggressive in pursuing full employment and be willing to tolerate moderate inflation risk," he added, discussing how Yellen would balance the Fed's twin objectives of promoting jobs and limiting inflation. But, he added, Yellen would be unlikely to allow inflation, or rising prices, to move much beyond the Fed's 2 percent target.

Obama will announce Yellen's nomination at the White House on Wednesday afternoon, and the two will be joined by outgoing Fed Chairman Ben Bernanke.