Ben S. Bernanke for the first time pledged that the Federal Reserve will buy bonds until the economy gets closer to his goals, cementing his place as the Fed's most innovative chairman and signaling the battle against unemployment eclipses any concerns about inflation for now.

The central bank yesterday announced its third round of large-scale asset purchases since 2008, with the difference that it didn't set any limit on the ultimate amount it would buy or the duration of the program. Instead, Bernanke said stimulus will be expanded until the Fed sees “sustained improvement” in the labor market.

Bernanke is “going to fight and fight until he sees a real improvement in the economy,” said Ethan Harris, co-head of global economics research at Bank of America Corp. in New York. “He's not going to let his critics stop him. He believes quantitative easing can help the economy and the Fed can avoid inflation, so he'll just keep at it until there's a real turn in the economy.”