Rates on 15- and 30-year fixed-rate mortgages fell for a fifth consecutive week to new lows, Freddie Mac said in releasing the results of its weekly Primary Mortgage Market Survey.

The 30-year fixed-rate mortgage averaged 4.71 percent with an average 0.7 point for the week ending Dec. 3, down from 4.78 percent last week and 5.53 percent a year ago. That's a new record dating back to 1971, when Freddie Mac began the survey.

The 15-year fixed-rate mortgage averaged 4.27 percent with an average 0.6 point, down from 4.29 percent last week and 5.77 percent a year ago. Rates on 15-year fixed-rate mortgages have never been lower since Freddie Mac started tracking them in 1991.

The 5-year Treasury-indexed hybrid adjustable-rate mortgage (ARM) loan averaged 4.19 percent this week, with an average 0.6 point, up slightly from last week's record low of 4.18 percent, but down from 5.77 percent a year ago.

The 1-year Treasury-indexed ARM averaged 4.25 percent this week with an average 0.6 point, down from 4.35 percent last week and 5.02 percent a year ago. The 1-year ARM has not been this low since the week ending June 30, 2005, when it averaged 4.24 percent.

Those rates are for prime borrowers taking out loans with 20 percent downpayments. Borrowers taking out loans too large or risky for purchase or guarantee by Freddie Mac can expect to pay more.

A Federal Reserve program that's helped keep mortgage rates low through purchases of up to $1.25 trillion in mortgage-backed securities issued by Fannie Mae, Freddie Mac and Ginnie Mae is scheduled to wind down at the end of March 2010.

The Mortgage Bankers Association last month projected that 30-year fixed-rate mortgages will hit 5.4 percent next year, 6 percent in 2011, and 6.3 percent in 2012 (see story).