Federal Reserve Bank of Philadelphia President Charles Plosser said new bond buying announced by the Fed this month probably won't boost growth or hiring and may jeopardize the central bank's credibility.

"We are unlikely to see much benefit to growth or to employment from further asset purchases," Plosser said in a speech today at the district bank in Philadelphia. "Conveying the idea that such action will have a substantive impact on labor markets and the speed of the recovery risks the Fed's credibility."

The Federal Open Market Committee said Sept. 13 that it will undertake a third round of quantitative easing by purchasing mortgage-backed securities at a pace of $40 billion per month until labor markets "improve substantially." Policy makers are using unconventional tools to attack a jobless rate stuck above 8 percent since February 2009.