WASHINGTON — Average U.S. rates for 30-year and 15-year fixed mortgages fell to fresh record lows this week, making home-buying and refinancing more affordable than ever for those who can qualify.

Mortgage buyer Freddie Mac said this morning that the rate on the 30-year loan ticked down to 3.83 percent. That’s the lowest since long-term mortgages began in the 1950s and below the previous record rate of 3.84 percent reached last week.

The 15-year mortgage, a popular option for refinancing, dropped to 3.05 percent, also a record. That’s down from last week’s previous record of 3.07 percent.

But cheaper mortgage rates haven’t done much to boost home sales. Rates have been below 4 percent for all but one week since early December.

Yet sales of both previously occupied homes and new homes fell in March.