The Fed needs to drive down borrowing rates because the economy isn't growing fast enough to reduce high unemployment, Bernanke said in a speech to the Economic Club of Indiana. The unemployment rate is 8.1 percent.

Low rates could also help shrink the federal budget deficit by easing the government's borrowing costs and generating tax revenue from stronger growth, Bernanke argued.

The chairman cautioned Congress against adopting a law that would allow it to review the Fed's interest-rate policy discussions. The House has passed legislation to give Congress' investigative arm broader authority to audit the Fed, including reviewing its interest-rate policymaking. The Senate hasn't adopted the bill.

Bernanke warned that such a step would improperly inject political pressure into the Fed's private deliberations and make officials less likely to act.

His speech follows the Fed's decision at its Sept. 12-13 meeting to launch a new mortgage-buying program to try to help boost the housing market, spur hiring and accelerate economic growth. The Fed said it would keep buying the bonds until the job market showed substantial improvement. It also decided to keep its benchmark short-term interest rate near zero through at least mid-2015.

In his speech, Bernanke sought to reassure investors that the Fed's timetable for keeping rates low "doesn't mean we expect the economy to be weak through 2015." Rather, he said the Fed expects to keep rates low well after the economy strengthens.

Bernanke spoke two days before President Obama and GOP challenger Mitt Romney will hold a debate in which the economy is the central theme. And on Friday, the government will release its September jobs report. Economists expect only modest hiring gains and continued unemployment above 8 percent.

The U.S. economy is still struggling more than three years after the Great Recession ended. High unemployment and weak pay growth have made consumers more cautious about spending, which has hurt manufacturing and slowed broader growth.

Bernanke reiterated his argument that lower rates boost growth by helping increase prices of stocks, homes and other assets. Greater household wealth tends to make consumers and businesses more willing to spend.

Bernanke noted that when the Fed launched its first round of bond buying in late 2008, the average rate on a 30-year fixed-rate mortgage was a little above 6 percent. Today, the rate is 3.4 percent, the lowest since long-term mortgages began in the 1950s.

Still, the housing market's recovery remains slow, in part because many Americans lack the credit to qualify for a mortgage or can't afford the larger down payments now required.

The Fed's decision last month to launch a new mortgage-buying program was approved by its policy committee, 11-1. Jeffrey Lacker, head of the Federal Reserve Bank of Richmond, cast the lone dissenting vote. Lacker has argued that further bond buying won't likely provide much economic help and risks igniting inflation in the future.

Charles Plosser, president of the Fed's Philadelphia regional bank, and Richard Fisher, president of the Fed's Dallas regional bank, have also been critical of the Fed's bond purchases. Plosser and Fisher do not have votes on the Fed's policy committee this year but take part in the discussions.

At the same time, one Fed official who had been skeptical of the bond buying now appears more open to it. Narayana Kocherlakota, president of the Minneapolis Fed, has signaled that he's grown more concerned about the economy's sluggish growth. In a speech a week after last month's policy meeting, Kocherlakota said the Fed should fight high unemployment with an even more aggressive approach than it announced.

Still, like Plosser and Fisher, Kocherlakota lacks a vote on the Fed's policy committee this year.