The average interest rate on 30-year fixed-rate mortgages dropped to 6.04 percent for the week ending Dec. 13, Freddie Mac reported Thursday in its weekly nationwide survey. That was down from 6.19 percent in the previous week.

This week's rates marked the first time rates on 30-year, 15-year and one-year adjustable rate mortgages fell since the week ending Nov. 15.

At that time, rates on 30-year mortgages dropped to 5.94 percent, the lowest level since the mortgage giant began tracking them in 1971.

Rates on 15-year fixed-rate mortgages, a popular option or refinancing, dipped to 5.46 percent this week, down from last week's 5.60 percent.

Low mortgage rates this year have been feeding a refinancing boom. The extra monthly cash consumers are saving by refinancing their mortgages at lower interest rates is helping to support consumer spending, which has been the main force keeping the economy going this year.

Home sales -- powered by low mortgage rates -- are expected to post records this year .

"Freddie Mac's most recent economic forecast indicates that next year's housing sector, though slower than this year's, will nevertheless continue to thrive," said Frank Nothaft, Freddie Mac's chief economist.