The Federal Reserve pledged Wednesday to keep a key interest rate at a record low for an “extended period,” in a sign that the economy is growing but remains deeply dependent on government help.

The Fed said economic activity has “continued to pick up” and that the housing market also has grown stronger, a key ingredient to a sustained recovery.

But Fed Chairman Ben Bernanke and his colleagues warned that rising joblessness and hard-to-get-credit for many people and companies could restrain the rebound in the months ahead.

“Economic activity is likely to remain weak for a time,” they said.

Against that backdrop, the Fed kept the target range for its bank lending rate at zero to 0.25 percent. And ...