The average rate on a 30-year fixed rate mortgage edged up to 4.96 percent this week from 4.95 percent a week earlier, the mortgage finance company Freddie Mac said Thursday.

Rates dropped to a record low of 4.71 percent in December and have hovered around 5 percent since, kept down by the Fed's $1.25 trillion program to buy up mortgage securities issued by Freddie Mac and sibling company Fannie Mae.

The Fed said this week that this program would end on March 31, as expected. But some analysts fear that once the program ends, mortgage rates could rise. That could weaken the fragile recovery in housing and the overall economy. Still, the Fed has left the door open to extending the program if the economy weakens.

The central bank has been the dominant buyer of mortgage securities over the past year. Without the Fed's participation, "it may take a few weeks for the market to sort out whether there's enough demand to soak up the supply," said Greg McBride, senior financial analyst with Bankrate.com.

Freddie Mac collects mortgage rates on Monday through Wednesday of each week from lenders around the country. Rates often fluctuate significantly, even within a given day, often in line with long-term Treasury bonds.