The benchmark 30-year fixed-rate home mortgage in the U.S. fell to a national average of 5.17% this week, the lowest since Freddie Mac began its weekly rate survey in 1971.

With the Federal Reserve cutting its interest rates to near 0% and a continued decline in rates on the long-term Treasury notes that mortgages closely track, rates on other types of mortgages dropped again, though not as much as the 30-year.

"Interest rates for 30-year fixed-rate mortgage rates fell for the seventh consecutive week, moving these rates to the lowest since the survey began in April 1971," said Frank Nothaft, Freddie Mac chief economist. "The decline was supported by the Federal Reserve announcement on Dec. 16, when it cut the federal-funds target to a record low and stated it stood ready to expand its purchases of mortgage-related assets as conditions warrant."

The 30-year mortgage fell for a seventh consecutive week, from 5.47% a week ago. A year ago the 30-year averaged 6.14%.

The 15-year fixed-rate mortgage averaged 4.92%, down from last week when it averaged 5.20%. A year ago the 15-year loan averaged 5.79%. The 15-year mortgage hasn't been lower since April 1, 2004, when it averaged 4.84%.