More likely, he said, would be a pullback beginning in late summer or early fall if the economy sustains its momentum. Even if that happens, the Fed will remain extraordinarily accommodative by many other measures, with short-term interest rates staying very low.

In response to a question from Representative Kevin Brady, a Texas Republican who is chairman of the Joint Economic Committee, Mr. Bernanke said that whenever the stimulus began to taper off, it would not happen in an “automatic, mechanistic program. Any change would depend on the incoming data.”

Further evidence for a move in a few months, rather than weeks, came in an interview shown on Wednesday on Bloomberg TV with the president of the Federal Reserve Bank of New York, William C. Dudley, that seemed aimed at clearing up some of the confusion.

“I think three or four months from now you’ll have a much better sense of is the economy healthy enough to overcome the fiscal drag or not,” said Mr. Dudley, who is a close ally of Mr. Bernanke.

Outside the canyons of Wall Street and the world of Fed watchers, the difference between June and August or September might not appear significant. But with interest rates at historical lows, any move to cut back on bond purchases by the Fed would undoubtedly cause an uptick in bond yields. That would affect the huge market for government and corporate bonds and force stock market investors to recalibrate their positions.

When the trading day began on Wednesday, investors were in a buoyant mood, sending stock indexes higher as Mr. Bernanke began his testimony. Markets around the world have rallied this year on hopes that the Fed and other central banks will continue to support financial markets with monetary policies.

As the day went on, though, traders began to reconsider some of Mr. Bernanke’s comments. After the details of the Federal Open Market Committee meeting on April 30 and May 1 were released, many strategists said they were surprised by the number of voices inside the Fed calling for a slowdown in the stimulus effort in the near future.