Mr. Bernanke said the Fed, having kept short-term interest rates at nearly zero since 2008, had essentially four options:

It can purchase more government debt and long-term securities. It can try to coax down long-term interest rates by announcing its intention to keep short-term rates extremely low for even longer than the markets currently expect. It can lower the interest rate it pays on the funds banks hold at the Fed. And it can raise its medium-term target for inflation, which would discourage banks from sitting on their cash.

Mr. Bernanke suggested that the first of those options was the most likely, and all but ruled out the last two.

While the Fed committee that sets monetary policy was prepared to take new steps “if the outlook were to deteriorate significantly,” he said, it “has not agreed on specific criteria or triggers for further action.”

As Mr. Bernanke’s remarks were released publicly, stock prices immediately fell, a sign that investors were hoping for some concrete signs that the Fed would step in to try to bolster the economy. But as the market digested the chairman’s full remarks, prices rebounded and the Dow Jones industrial average rose 164.84 points, or 1.65 percent, to 10,150.65. The yield on the benchmark 10-year Treasury note rose to 2.64 percent, from 2.48 percent. The revised second-quarter growth data came after a week that showed that the economic retrenchment that began in the second quarter had spilled into the summer, with a sharp slowdown in new-home sales and a drop in sales of factory goods.