WASHINGTON — The average rate on 30-year fixed mortgages stayed this week at the lowest on record. Mortgage buyer Freddie Mac says the average was 3.66 percent, unchanged from last week and the lowest since long-term mortgages began in the 1950s.

The average rate on the 15-year mortgage slipped to 2.94 percent. That’s down from 2.95 percent last week and matches the record low 2.94 percent of three weeks ago.

The rate on the 30-year loan has been below 4 percent since December.

Low rates could provide some help to the economy if more people refinance. When people refinance at lower rates, they pay less interest and have more to spend.

Mortgage rates have been dropping because they tend to track the yield on the 10-year Treasury note. Uncertainty about Europe has led investors to buy more Treasury securities, considered safe investments. As demand for Treasurys increase, the yield falls.