Federal Reserve Chairman Ben Bernanke told a Senate panel Wednesday a potential wave of defaults in commercial real estate may present a difficult challenge for the economy, if additional measures are not taken to aid the market.

Bernanke urged lenders to modify problem mortgages to avert defaults.

The most questioned topic that lawmakers had for Bernanke was about the current state of the commercial real estate. Bernanke said today in the Senate and yesterday at the House Financial Services Committee that it was still too soon to tell how effective the Fed's main initiative in the area will be.