WASHINGTON— The average rate on the 30-year fixed mortgage fell again, this time dropping below 3.5 percent for the first time on records dating back 60 years.

Mortgage buyer Freddie Mac said Thursday that the rate on the 30-year loan declined to 3.49 percent. That’s down from 3.53 percent last week and the lowest since long-term mortgages began in the 1950s.

The average rate on the 15-year fixed mortgage, a popular refinancing option, dipped to 2.8 percent. That’s below last week’s previous record of 2.83 percent.

The rate on the 30-year loan has fallen to or matched record-low levels in 13 of the past 14 weeks.

Cheaper mortgages have helped drive a modest but uneven housing recovery this year. Sales of new and previously occupied homes fell in June but were higher than the same month last year. Home prices have started to stabilize in many large markets. And builders are more confident and are putting up more houses than they have in nearly four years.

Low mortgage rates could provide some help to the economy if more people refinance. When people refinance at lower rates, they pay less interest on their loans and have more money to spend.

Many homeowners use the savings on renovations, furniture, appliances and other improvements, which help drive growth.

Fewer Americans signed contracts to buy homes in June, the National Association of Realtors said in a separate report Thursday. The group’s index of sales agreements fell to 99.3, down from May’s reading of 100.7.

A reading of 100 is considered healthy. The index is 9.5 percent higher than it was a year ago. There’s generally a one- to two-month lag between a signed contract and a completed deal.