WASHINGTON (AP) — The average U.S. rate for the 30-year fixed mortgage fell to a record low for a fourth straight week. Cheap mortgages have helped boost home sales modestly this year.

Mortgage buyer Freddie Mac said Thursday that the rate on the 30-year loan dipped to 3.78 percent. That's down from 3.79 percent last week and the lowest since long-term mortgages began in the 1950s.

The average rate on 15-year fixed mortgage, a popular option for refinancing, held steady at 3.04, matching the record low hit last week.

The average rate on the 30-year loan has been below 4 percent since early December. Lower rates are a key reason the housing industry is flashing signs of a recovery five years after the bubble burst.

In April, sales of both previously occupied homes and new homes rose near two-year highs. Builders are gaining more confidence in the market, breaking ground on more homes and requesting more permits to build single-family homes later this year.

A better job market has also made more people open to buying a home. Employers have added 1 million jobs in the past five months. The unemployment has dropped a full percentage point since August, from 9.1 percent to 8.1 percent in April.

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. 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.

To calculate average rates, Freddie Mac surveys lenders across the country on Monday through Wednesday of each week.

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, down from 0.7 last week. The fee for 15-year loans was 0.7, unchanged from last week,

The average rate on one-year adjustable rate mortgages was 2.75 percent last week, down from 2.78 percent the previous week. The fee for one-year adjustable rate loans was 0.4, down from 0.5 last week.