WASHINGTON – Average U.S. rates on 30-year and 15-year fixed mortgages dropped to record lows again last week, with the 15-year loan dipping below 3 percent for the first time ever.

Low rates have helped brighten the outlook for home sales this year. They have made home-buying and refinancing more attractive to those who can qualify.

Mortgage buyer Freddie Mac said Thursday that the average rate on the 30-year loan fell to 3.75 percent. That’s down from 3.78 percent the previous week and the lowest since long-term mortgages began in the 1950s.

The 15-year mortgage, a popular refinancing option, slipped to 2.97 percent. That’s down from 3.04 percent a week earlier.

Rates on the 30-year loan have been below 4 percent since early December. The low rates are a key reason the housing industry is showing modest signs of a recovery this year.

Still, the pace of home sales remains well below healthy levels. Economists say it could be years before the market is fully healed.

Many people are having difficulty qualifying for home loans or can’t afford larger down payments required by banks. Some would-be home buyers are holding off because they fear that home prices could keep falling.

Mortgage rates have been dropping because they tend to track the yield on the 10-year Treasury note, which fell last week to a 66-year low. Uncertainty about how Europe will resolve its debt crisis has led investors to buy more Treasury securities, which are considered safe investments. As demand for Treasurys increase, the yield falls.

The average does not 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 loans was 0.8, unchanged from a week earlier. The fee for 15-year loans also was steady, at 0.7.