WASHINGTON — Ben Bernanke isn't a household name — yet.

But if all goes well, he'll be the next chief of the Federal Reserve, wielding enormous power over the economy and the portfolios of millions of investors large and small.

Bernanke, a plain-speaking former economics professor, was chosen yesterday by President Bush to replace Alan Greenspan. Largely unknown to the general public when he took over the Fed in 1987, Greenspan has risen to iconic status.

Bush called him a "legend." And Bernanke promised to continue the policies of Greenspan, who steps down Jan. 31.

"Ben has done path-breaking work in the field of monetary policy, taught advanced economics at some of our top universities and served with distinction on the Fed's Board of Governors," said Bush, who was flanked by Bernanke and Greenspan during a brief White House ceremony. "He's earned a reputation for intellectual rigor and integrity. He commands deep respect in the global financial community."

Greenspan called Bush's choice "a distinguished appointment. Ben comes with superb academic credentials and important insights into the ways our economy functions."

It was the third time in as many years that Bush has turned to the 51-year-old Bernanke for a sensitive economic post. The president named him to the Fed board in 2002, then made him chairman of the president's Council of Economic Advisers earlier this year.

The nomination comes at a difficult time for Bush. His approval ratings are sagging, his choice of Harriet Miers for the Supreme Court is under attack, and his top political adviser — Karl Rove — is a central figure in the investigation of who leaked the name of an undercover CIA officer.

The initial reaction to Bernanke was positive. Academics, Republican and Democratic lawmakers, economists and other experts said Bernanke, a leading thinker on monetary policy, has impeccable academic credentials for the Fed post.

On Wall Street, the Dow Jones industrial average soared nearly 170 points, the best one-day showing in six months.

Bernanke (pronounced ber-NANK-ee) acknowledged that he has big shoes to fill, saying Greenspan "has set the standard for excellence in economic policymaking."

If he is approved to a four-year term as Fed chairman, Bernanke said, his first priority would be "to maintain continuity" with the policies and strategies during the Greenspan era. He pledged to do all he could to ensure "the continued prosperity and stability of the American economy."

The Fed determines interest rate policies that affect any person or business that borrows money. Its decisions — along with utterances from the Fed chief — can influence financial markets around the globe.

As the country's second-longest serving Fed chairman, the 79-year-old Greenspan has attained cult-like status and often is referred to as the second-most important person in Washington. On Greenspan's watch, the U.S. economy grew from March 1991 to March 2001, the longest continuous expansion in history. The two recessions during his tenure — in 1990-91 and in 2001 — were mild.