Bernanke acknowledged those trends. He noted that the economy, after growing at an annual rate of 2.5 percent in the second half of 2011, slowed to roughly 2 percent in the first three months of this year and likely weakened further in the April-June period.

The economy will likely continue to expand moderately, he said. But the meager growth would slow further if Europe's debt crisis worsens or if Congress doesn't address an impending budget crisis before the end of the year.

"Although declines in energy prices are now providing some support to consumers' purchasing power, households remain concerned about their employment and income prospects and their overall level of confidence remains relatively low," Bernanke said in his testimony.

Even if the Fed announces another round of bond purchases, some economists question how much that would help. They note that mortgage rates and other key interest rates are already at record-low levels.