WASHINGTON  A subtle but significant shift appears to be occurring within the Federal Reserve over the course of monetary policy as the economic recovery is weakening.

On Thursday, James Bullard, president of the Federal Reserve Bank of St. Louis, warned that the Fed’s policies were putting the economy at risk of becoming “enmeshed in a Japanese-style deflationary outcome within the next several years.”

The warning by Mr. Bullard, who is a voting member of the Fed committee that determines interest rates, came days after Ben S. Bernanke, the Fed chairman, said the central bank was prepared to do more to stimulate the economy if needed, though it had no immediate plans to do so. On Friday, the government will release its estimate of gross domestic product for the second quarter of this year.

At the Fed, Mr. Bullard had been associated with the camp that sees inflation, the central bank’s traditional enemy, as a greater threat than deflation brought on by anemic growth. Until now he had not been an advocate for large-scale asset purchases to reinvigorate the economy.