These conclusions remain deeply controversial. Many monetary economists take the view that central banks should focus exclusively on controlling inflation, which creates an environment conducive to economic growth and job creation. Some argue that the Fed’s efforts to spur job growth by decreasing long-term borrowing costs will inevitably result in higher inflation, eventually reducing growth and employment.

And it is clear that many economic problems are beyond the reach of monetary policy. The Fed cannot force Congress to budget. It cannot repair consumer credit nor change Europe into something more sensible. Even the most optimistic analysts do not think its efforts will return unemployment to its precrisis level.

Mr. Bernanke’s predecessor, Alan Greenspan, once told his board that he did not want to mention job creation as a policy objective because the Fed would be making a promise that it lacked the power to keep. Mr. Bernanke, by contrast, has decided to make the promise and try to deliver on it — not just because he thinks that it is within the Fed’s power, but at least in part because he thinks it is important to try.

“Up until now the Fed has been very cautious in interpreting the dual mandate,” said Stephen D. Oliner, a scholar at the American Enterprise Institute who worked as a staff economist at the Federal Reserve for more than 25 years. “They have not really aggressively pursued a trade-off between inflation and unemployment. And what they’re now doing is they’re saying we’re kind of rebalancing to put greater weight on unemployment.”

The evolution of the Fed’s thinking has been visible in its public statements. It made no direct reference to the labor market in its policy statements until December 2008, according to a review by Daniel L. Thornton, an economist at the Federal Reserve Bank of St. Louis. In January, the Fed for the first time cited the unemployment rate as a primary reason for a new policy.