Washington ? For the fourth week in a row, rates on 30-year mortgages fell to a new low, good news for a housing market that has been one of the few bright spots for the struggling economy.

The average interest rate on 30-year fixed-rate mortgages dropped to 5.61 percent for the week ending March 14, Freddie Mac, the mortgage company, reported Thursday in its weekly nationwide survey.

That surpassed the previous record low rate of 5.67 percent set last week. The new rate marked the fourth week in a row and the fifth time this year that rates on the benchmark mortgage dipped to a new weekly low.

This week’s rate was the lowest since Freddie Mac began tracking 30-year mortgage rates in 1971. Records that reach back earlier than Freddie Mac’s indicate that rate is the lowest since the early 1960s.

Rates for 15-year fixed-rate mortgages dipped this week to 4.93 percent, compared with 5.01 percent last week.