WASHINGTON » Average U.S. rates on fixed mortgages fell sharply this week and moved closer to historic lows, keeping home-buying and refinancing attractive.

Mortgage buyer Freddie Mac said today that the average rate for the 30-year fixed loan fell to 3.43 percent from 3.54 percent last week. That’s near the 3.31 percent reached in November, which was the lowest on records dating to 1971.

The average rate on the 15-year fixed mortgage dipped to 2.65 percent from 2.74 percent last week. That’s slightly above the record low of 2.63 percent, also reached in November.

Low mortgage rates are helping sustain a housing recovery that began last year. Home sales and residential construction are up, prices are rising and more Americans are refinancing. That’s helped the broader economy.

Mortgage rates have been low because they tend to track the yield on the 10-year Treasury note. The yield has fallen in recent weeks and went as low as 1.71 percent April 5, after a weak report on March hiring drove investors to seek the safety of a U.S. Treasury bonds. When demand rises, the yield falls.

Today the yield was up to 1.79 percent, still low by historical standards.

To calculate average mortgage rates, Freddie Mac surveys lenders across the country on Monday through Wednesday each week. The average doesn’t include extra fees, known as points, which most borrowers must pay to get the lowest rates. One point equals 1 percent of the loan amount.

The average fee for 30-year mortgages was unchanged at 0.8 point. The fee for 15-year loans also was steady, at 0.7 point.

The average rate on a one-year adjustable-rate mortgage edged down to 2.62 percent from 2.63 percent last week. The fee for one-year adjustable-rate loans slipped to 0.3 point from 0.4.

The average rate on a five-year adjustable-rate mortgage fell to 2.62 percent from 2.65 percent. The fee held at 0.5 point.