Chairman Ben Bernanke said Wednesday that the U.S. economy still needs help from the Federal Reserve's low interest rate policies.

Bernanke told the National Bureau of Economic Research that because unemployment remains high and inflation is below the Fed's target, the policies are still necessary. He also said the economy is also being held back by higher taxes and federal spending cuts.

``If you put all of that together, you can only conclude that highly accommodative monetary policy for the foreseeable future is what is needed for the U.S. economy,'' Bernanke said.

Stock index futures rose as Bernanke spoke. The Standard & Poor's index futures were up eight points, or 0.5 percent, at 1,656 as of 5:40 p.m. Eastern Daylight Time _ shortly after Bernanke wrapped up his remarks.

Bernanke's comments were his latest effort to stress that the Fed will continue to stimulate the economy, even after it begins to slow its bond purchases. The Fed plans to keep its investment holdings constant to avoid causing long-term rates to rise too quickly. It also plans to keep short-term rates at record lows at least until unemployment slides to 6.5 percent.

And Bernanke has said 6.5 percent unemployment is a threshold, not a trigger: The Fed might decide to keep its benchmark short-term rate near zero even after unemployment falls that low.

Unemployment is now 7.6 percent.

On Wednesday, Bernanke didn't signal any changes in the Fed's bond-buying program, which have kept long-term interest rates low and encouraged more borrowing and spending. But he defended recent comments he made after the Fed's June meeting.

At his June 19 news conference, Bernanke said the Fed would likely slow its bond purchases later this year and end them around mid-2014 if the economy continued to strengthen. The Fed has been buying $85 billion in Treasury and mortgage bonds each month since late last year.

Stocks and bonds plunged in the days after his remarks. Some critics said the Fed bungled its communications strategy.

Bernanke asked his audience to consider what might have happened if the Fed had given no signals on when the bond buying might be curtailed. He said that might have led to an increase in risk-taking on the part of investors ``reflecting an expectation for an infinite'' program of bond purchases.

``Explaining what we are doing may have avoided a much more difficult situation at another time,'' he said.

Bernanke also did not provide any clues on his own future. Many expect he will leave when his current term ends in January.

When asked about his legacy, he said others would certainly judge his handling of the 2008 financial crisis. He also said the Fed, under his leadership, has made significant strides in providing the public with more information on how the central bank operates. (AP)