WASHINGTON (AP) — Fixed mortgage rates fell to the lowest level in six decades for the second straight week. But few Americans can take advantage of the historically low rates.

Freddie Mac says the average rate on the 30-year fixed mortgage fell to 4.09 percent this week. That's the lowest rate seen since 1951.

The average rate on the 15-year mortgage, a popular refinancing option, fell to 3.30 percent, also a new low. Economists say it is likely the lowest rate on the 15-year ever.

Mortgage rates tend to track the yield on the 10-year Treasury note. Worries over Europe's debt crisis are pushing investors to shift money into safe Treasurys, forcing the yield lower.

Still, the cheap mortgage rates haven't helped home sales. Few would-be buyers can meet stricter loan requirements.