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

Mortgage buyer Freddie Mac said Thursday 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 it's 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.

Low 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.

There have been some positive signs in recent months. January and February made up the best winter for sales of previously occupied homes in five years. And builders are laying plans to construct more homes in 2012 than at any other point in past 3 1/2 years. That suggests some see the housing market slowly starting to turn around.