Fed Chairman Ben Bernanke told reporters Wednesday that the central bank had been caught off guard by recent signs of deterioration in the economy. And he said the troubles could continue into next year.

"We don't have a precise read on why this slower pace of growth is persisting," Bernanke said. He said the weak housing market and problems in the banking system might be "more persistent than we thought."

It was the Fed chief's most explicit warning yet that the economy will face serious challenges next year. For several months, he had said the factors working against economic growth appeared to be "transitory."

The Fed cut its forecast for economic growth this year to a range of 2.7 percent to 2.9 percent from an April forecast of 3.1 percent to 3.3 percent. It also cut its forecast for next year to a range of 3.3 percent to 3.7 percent from an earlier 3.5 percent to 4.2 percent. The Fed also said unemployment would stay higher than it had expected earlier.