WASHINGTON » Rates on 30-year mortgages matched the lowest level in decades, and rates on 15-year loans dropped to their lowest point in nearly 20 years.

Mortgage buyer Freddie Mac said yesterday the average rate for 30-year fixed loans fell to 4.32 percent, the lowest on records dating back to 1971. That’s down from 4.37 percent the previous week and equal to the average rate reached four weeks ago.

The average rate on 15-year fixed loans fell to 3.75 percent, the lowest on records dating back to 1991.

Rates have been at or near the lowest levels in decades since spring as investors poured money into the safety of Treasury bonds, lowering their yield. Mortgage rates tend to track those yields.

In recent weeks, Treasury yields have dipped as bond traders bet that the Federal Reserve will soon boost its Treasury purchases in the hope of giving the economy a lift. That has pushed down rates.

Still, historically low rates have done little to boost the struggling housing market, which had its worst summer in more than a decade.