Washington ? Rates for 30-year mortgages dipped to a new low this week, providing even more fuel for the mortgage refinancing boom.

In a nationwide survey released Thursday, Freddie Mac, the mortgage company, reported that the average interest rate on a 30-year fixed-rate mortgage dropped to 6.22 percent, the lowest level in 32 years of record keeping.

This week’s rate surpassed the previous low of 6.31 percent set last week. Last week’s rate had bested the prior low of 6.34 percent reached in July.

Low mortgage rates are feeding a boom in mortgage refinancing. Savings or extra cash coming out of refinancing deals is helping to support consumer spending and offsetting some potentially negative factors, such as the volatile stock market and eroding consumer confidence, economists said.

Refinancing activity last week represented 68.8 percent of mortgage loan applications, up from 68.4 percent the previous week, the Mortgage Bankers Association of America reported Wednesday.

The average interest rate on 15-year mortgages, a popular option for refinancing, fell to 5.63 percent this week, the lowest level since Freddie Mac began tracking rates in August 1991. That compared with last week’s rate of 5.69 percent.

On one-year adjustable-rate mortgages, lenders were asking an average initial rate of 4.39 percent, up slightly from 4.37 percent the previous week. Last year this time, one-year ARMs averaged 5.71 percent.

The rates do not include add-on fees known as points.

Thirty-year mortgages and one-year ARMs each carried an average 0.6 point this week, while 15-year mortgages carried an average 0.5 point.

Mortgage rates have been falling amid growing signs of a sluggish economic recovery and a roller-coaster stock market that has sent investors to the bond market, helping to push long-term interest rates down.