Rates on 30-year mortgages fell to the lowest level in decades for the ninth time in 12 weeks, pushed down by traders anticipating a move by the Federal Reserve to pump more money into the economy.

The average rate for 30-year fixed loans dropped to 4.27 percent, mortgage buyer Freddie Mac said Thursday. That's the lowest on records dating back to 1971, and down from 4.32 percent the previous week.

The average rate on 15-year fixed loans, a popular choice for refinancing, dropped to 3.72 percent from 3.75 percent. That was lowest on records dating back to 1991.

Rates have mostly fallen since spring as investors shifted money into the safety of Treasury bonds, lowering their yield. Mortgage rates tend to track those yields.

The 30-year rate was 5.08 percent at the beginning of April, while the 15-year rate was 4.39 percent.

In recent weeks, Treasury yields have dropped as investors predict that the Federal Reserve will soon boost its Treasury purchases to help boost the economy. That has pushed down rates.

The yield on the closely watched 10-year yield reached its lowest point this year at 2.39 percent Wednesday following a surprisingly weak employment report.

However, historically low rates haven't helped the struggling housing market, which recorded its worst summer in more than a decade.

Sales this fall are not expected to improve that much. Job concerns have kept many people from buying homes. Tighter credit standards have also dissuaded many would-be buyers from purchasing. Experts also expect the worst-hit cities to face more foreclosures and other distressed sales.

To calculate average mortgage rates, Freddie Mac collects rates from lenders around the country on Monday through Wednesday of each week. Rates often fluctuate significantly, even within a given day.

Rates on five-year adjustable-rate mortgages averaged 3.47 percent, down from 3.52 percent a week earlier. Rates on one-year adjustable-rate mortgages fell to an average of 3.40 percent from 3.48 percent.

The rates do not include add-on fees known as points. One point is equal to 1 percent of the total loan amount. The nationwide fee for loans in Freddie Mac's survey averaged 0.8 a point for 30-year mortgages. It averaged 0.7 of a point for 15-year and 1-year mortgages and 0.6 of a point for 5-year mortgages.