WASHINGTON » The average U.S. rate on a 30-year fixed mortgage slipped this week and stayed near its record low, a trend that’s helped boost home sales and refinancing.

Mortgage buyer Freddie Mac says the rate on the 30-year loan declined to 3.39 percent from 3.41 percent last week. Four weeks ago, the rate touched 3.36 percent, the lowest level on records dating to 1971.

The average on the 15-year fixed mortgage, often used for refinancing, fell to 2.70 percent. That’s down from 2.72 percent last week and close to the record low of 2.66 percent reached two weeks ago.

The low rates have helped drive a modest housing recovery. Rates have fallen further since the Federal Reserve started buying mortgage bonds in September.