Washington ? The Federal Reserve sought Wednesday to defuse fears that the trillions it’s spending to revive the economy could spark inflation later on. But Wall Street didn’t seem to buy it.

Fed Chairman Ben Bernanke and his colleagues said that despite an easing of the recession, the economy remains frail enough to keep inflation at bay.

Fed policymakers held a key bank lending rate at a record low of between zero and 0.25 percent and pledged to keep it there for “an extended period” to help brace the economy. The Fed made no new commitment to expand its purchases of government bonds and mortgage securities, to try to drive down rates on consumer debt. That rattled bond investors who fear the prospect of higher interest rates.