"Because our asset purchases depend on economic and financial developments, they are by no means on a preset course," he told the House Financial Services Committee during the first of two days of testimony this week on the Fed's semi-annual report. He will testify Thursday before the Senate Banking Committee.
Stocks edged higher during and after Bernanke's testimony. The Dow Jones industrial average was up 10 points in afternoon trading, and broader indexes also gained.
The yield on the benchmark 10-year Treasury note fell to 2.49 percent, down from 2.55 percent before Bernanke's comments were made public.
Bernanke's remarks were his latest attempt to calm markets, which have gyrated wildly since the Fed's June meeting.
Last month stocks plunged after Bernanke said the Fed could slow the bond purchases later this year and end them next year if the economy strengthens. Since them, Bernanke and other Fed members have stressed that any change in policy depends on improvement in the job market and economy, not a target date
On Wednesday, Bernanke stuck closely to that more dovish theme. He noted that the job market has made some progress but the Fed wants to see "substantial progress" before reducing the bond buys.
"Despite these gains, the job situation is far from satisfactory," he said.
Bernanke also said the Fed plans to keep its benchmark short-term interest rate near zero as long as unemployment is above 6.5 percent. And the Fed could hold the rate down even after it falls below 6.5 percent, he said, if unemployment falls because more people are leaving the workforce. The government counts people as unemployed only if they are actively looking for a job.
The job market has accelerated since the bond buying began in September. Employers have an average of 202,000 jobs a month this year, up from 180,000 in the previous six months. Still, unemployment remains high at 7.6 percent and economic growth has been weak for the past three quarters.
Bernanke said he thought the unemployment rate would then be about 7 percent when the bond buying program ends.
"What Bernanke did today is try to contain the damage from what was a communication misstep in June and I think he succeeded," said Brian Bethune, an economics professor at Gordon College in Wenham, Mass. "The Fed in June saw that even the smallest hint of a change in Fed policy can turn out to be extremely powerful in terms of its impact on financial markets."
Bethune predicts the Fed will hold off on any policy change in September because there will not be enough data to show that economic growth has strengthened. Bethune said the earliest the Fed could announce a reduction in bond purchases would likely be December.
Still, other economists believe the Fed is still on track to slow its purchases in September.
Paul Dales, senior U.S. economist for Capital Economics, said Bernanke's remarks did not alter that view. Of course, Dales said Bernanke made it known that any change would depend heavily on how the economy's health.
"We don't think this forward guidance could be much clearer," Dales said.