WASHINGTON (AP) — Fixed mortgage rates fell this week to the lowest levels in six decades. But few Americans can take advantage of the rates to refinance or buy a home.

The average rate for the 30-year fixed mortgage fell to 4.12 percent, down from 4.22 percent, Freddie Mac said Thursday. It's the lowest level on records dating back to 1971. Freddie Mac said the last time rates were cheaper was 1951, when most long-term home loans lasted just 20 or 25 years.

The average rate on a 15-year fixed mortgage, a popular refinancing option, fell to 3.33 percent from 3.39 percent. That's the lowest on records dating to 1991 and likely the lowest ever, according to economists.

Mortgage rates tend to track the yield on the 10-year Treasury note, which fell to an all-time low this week. An uncertain outlook for the U.S. economy has led many investors to shift money out of stocks and into the safety of Treasurys, lowering the yield.

Record-low mortgage rates have done little to energize the depressed housing market.

Over the past year, the average rate on the 30-year fixed mortgage has been below 5 percent for all but two weeks. That compares with five years ago, when the average 30-year fixed rate was near 6.5 percent.

Yet sales of new homes are on pace to finish the year as the lowest on records dating back a half-century. The pace of re-sales is shaping up to be the worst in 14 years.

Many Americans are in no position to buy. High unemployment, scant wage gains and large debt loads have kept them away.

Others can't qualify for the lowest rates. Banks are insisting on higher credit scores and 20 percent down payments for first-time buyers. Many repeat buyers have too little equity invested in their homes to meet loan requirements.

"Low rates are great, but the real issue is that the pool of people who can get a loan or refinance is small," said Greg McBride, Bankrate.com's senior financial analyst."

Roughly 40 percent of U.S. households have the necessary credit scores above 700 to get a prime mortgage rate, according to an Associated Press analysis of Fair Isaac Corp., or FICO, data.

A bigger issue is just half of Americans say they'll ever be able to save enough money for any type of down payment, let alone one as high as 20 percent, according to a survey by the National Foundation for Credit Counseling.

Nearly a third of homeowners have nearly zero equity or are underwater in their mortgage, according to the real estate research firm CoreLogic. That leaves then unable to refinance because of lender-imposed limits and the cost of extra fees.

Increased refinancing activity isn't providing much economic benefit. Without much equity, few are drawing money out for home-improvement projects or other big expenditures.

Many people must also pay extra fees to get the low mortgage rates. Those fees are known as points. One point is equal to 1 percent of the total loan amount.

The average fees for the 30-year held steady at 0.7 point. The 15-year fixed loans and 5-year and one-year adjustable rate loans were all at 0.6 point.

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

The average rate on a five-year adjustable-rate mortgage was unchanged at 2.96 percent. That's the lowest rate on records dating to January 2005. It was the sixth straight week of record lows for this type of loan.

The average rate for the one-year adjustable-rate mortgage fell to 2.84 percent. That's the lowest on records going back to 1984.