WASHINGTON (AP) _ Mortgage rates fell further this week with the rate on a 30-year mortgage remaining below the 7 percent threshold for a second consecutive week.

The average interest rate on 30-year fixed-rate mortgages dipped to 6.91 percent, down slightly from 6.92 percent last week, according to the nationwide survey released Thursday by Freddie Mac, the mortgage company.

It marked the lowest level for 30-year mortgages since last March when they dropped below 7 percent for four weeks. Analysts expect this level, which has been seen for only brief periods over the last 25 years, is likely to spur another burst of home refinancing and help support home sales, which have held up surprisingly well this year despite the sharp economic slowdown.

Fifteen-year mortgages, a popular option for refinancing, also declined this week to 6.47 percent from 6.48 percent the previous week.

A year ago, rates for 30-year mortgages were more than a percentage point higher 7.99 percent and rates for 15-year mortgages averaged 7.72 percent.

On one-year adjustable-rate mortgages, lenders were asking an average initial rate of 5.68 percent, down from 5.71 percent the previous week. Last year at this time, ARMs stood at 7.37 percent.

These rates do not include add-on fees known as points, which averaged around 1 percent of the loan amount for all three types of mortgages.