WASHINGTON — Rates on 30-year mortgages, after declining for three weeks, were unchanged this week while other types of mortgages dipped lower on expectations of slower economic growth in coming months.

Mortgage giant Freddie Mac reported yesterday that the nationwide average for rates on 30-year, fixed-rate mortgages remained frozen at 5.71 percent this week, the same as last week. The 30-year rate had fallen for three weeks, pushing it down to the lowest point since mid-July.

Analysts said continued low mortgage rates were helping to keep housing sales near record levels and they predicted rates would likely fall further in coming weeks as the drag on growth from Hurricane Katrina lessens fears in the bond market that stronger growth might trigger inflation pressures.

Frank Nothaft, chief economist at Freddie Mac, said that while he expected economic growth to be a bit slower this year, the pace of activity next year will be higher, reflecting increased federal spending on rebuilding and lower interest rates brought on by the disaster.

While lower mortgage rates will be a break for home buyers, Nothaft said they would be offset somewhat by higher prices for building materials as demand increases to rebuild thousands of homes destroyed along the Gulf Coast.

He said those higher costs could add 2 percent to 3 percent to the price of new homes in coming months but that this would be balanced out by slightly lower mortgage rates.

Rates on 15-year, fixed-rate mortgages, a popular choice for refinancing a home mortgage, averaged 5.30 percent this week, down from 5.32 percent last week.

One-year adjustable rate mortgages edged down slightly to 4.45 percent from 4.48 percent last week. In mid August, one-year ARMs hit their highest level in more than three years at 4.58 percent.

Rates on five-year hybrid adjustable rate mortgages averaged 5.24 percent this week, unchanged from last week.

The nationwide averages for mortgage rates do not include add-on fees known as points. The one-year ARM had an average fee of 0.7 point while all the other categories carried a fee of 0.6 point.

A year ago, 30-year mortgages averaged 5.83 percent, 15-year mortgages were at 5.22 percent and one-year ARMs averaged 4.00 percent. Freddie Mac does not have historical data on the five-year ARM which it began tracking this year.