WASHINGTON — The Federal Reserve’s chairman, Ben S. Bernanke, emphasized on Wednesday that the central bank remains committed to bolstering the economy, insisting that any deceleration in the Fed’s stimulus campaign will happen because it is achieving its goals, not because it has lowered its sights.

Mr. Bernanke said he still expected to reach that point in the coming months but, in what may have been his final appearance before the House Financial Services Committee, he cautioned that Congress itself posed the greatest risk to growth.

“The risks remain that tight federal fiscal policy will restrain economic growth over the next few quarters by more than we currently expect, or that the debate concerning other fiscal policy issues, such as the status of the debt ceiling, will evolve in a way that could hamper the recovery,” he told the committee.

The sluggish economy has been a constant background for Mr. Bernanke’s biannual testimony. Unemployment, at 7.6 percent, remains stubbornly above the Fed’s goals. Inflation has sagged to the lowest pace on record. Growth continues at a “modest to moderate pace,” the Fed said Wednesday in its monthly beige book survey of economic conditions across the country, released separately from Mr. Bernanke’s testimony.