The central bank’s stimulus campaign has “driven up asset prices without adding significantly to job creation,” said Mark Calabria, director of financial regulation at the Cato Institute. He said low borrowing costs might be making it easier for companies to invest in technology rather than hiring workers.

The economy remains scarred by the collapse of the housing bubble and the consequent 2008 financial crisis. Growth is tepid, unemployment high, inflation sluggish. Ms. Yellen acknowledged those problems, but reiterated the Fed’s upbeat forecast.

“The economic recovery gained greater traction in the second half of last year,” she said, citing the growth of spending by consumers and businesses. She said the Fed expected “economic activity and unemployment will expand at a moderate pace this year and next.”

Ms. Yellen acknowledged that she was “surprised” by disappointing estimates of job growth in December and January, but she cautioned against “jumping to conclusions” in assessing the longer-term trend. She noted the government would release an estimate of February job growth before the Fed’s March meeting.

She played down concerns about the consequences of Fed policy. Asked about the impact of low interest rates on savers, particularly the elderly, she said that the Fed could not raise rates without damaging the economy, and noted that low rates had a variety of effects. Retirees with savings accounts, for example, often own stocks too, which have soared in recent years.

Like her predecessor, Ms. Yellen said the Fed’s greatest concern was the risk of destabilizing financial markets. And like Mr. Bernanke, she said the Fed was watching closely but didn’t see problems yet. “I haven’t seen threats to financial stability that have built to the point of flashing orange or red,” Ms. Yellen said.

The Fed said in 2012 that it planned to keep short-term interest rates near zero at least as long as the unemployment rate remained above 6.5 percent. It has since said that it was likely to maintain that policy well past that threshold, but with the unemployment rate reaching 6.6 percent in January, some Fed officials have said there is a need for greater clarity about its plans.