The 30-year fixed-rate mortgage average of 5.71% was the only mortgage product that was unchanged from last week, according to Freddie Mac’s latest Primary Mortgage Market Survey.

The 15-year reportedly came in at 5.30%, edging down two basis points from a week earlier.

The 10-year Treasury note, which serves as the gauge for long-term mortgage rates, had the opposite effect as it traded at 100.91 with a 4.13% yield Thursday afternoon, worse than 101.69 and 4.03% a week ago.

The largest weekly decrease — down six BPS to 5.24% — occurred in the average for 5-year Treasury-indexed hybrid adjustable-rate mortgages, Freddie said.

The 1-year Treasury-indexed ARM average was reportedly 4.45% this week, slipping three BPS from a week ago. The weekly decline was more notable in the actual ARM index, the 1-year T-bill, which the Federal Reserve said fell 12 BPS to 3.73% as of Tuesday.

“Slightly lower mortgage rates” are on the horizon as Freddie chief economist Frank Nothaft expects near-term economic growth will “now be a bit weaker than had been anticipated, due in very large part to the disruption in economic activity brought on by Katrina last week.”

But “federal monies that will flow into the damaged areas and the lower interest rates brought on by the disaster will stimulate economic growth next year, making up for the slowdown in the last part of this year,” he added.

The panel of 100 mortgage “experts” surveyed by Bankrate.com this week was evenly split on whether rates would remain flat or go up over the next 35 to 45 days. In stark contrast to the outlook by Freddie’s Nothaft, nobody surveyed by Bankrate.com saw rates heading lower.

Mortgage application volume reversed a two-consecutive-week decline by improving 7% the week before Labor Day, the Mortgage Bankers Association reported.

The spark in application activity was led by an 8% increase in refinance loan requests, which apparently edged up the refi share of total applications to 45%, MBA said, and assisted by a 6% incline from the previous week in purchase money mortgage applications.

The group noted the volume of ARM applications is down 10% from a year ago, whereas the number of fixed-rate mortgage applications is up 23%. During that period the spread between the average 30-year fixed and 1-year ARM narrowed from 183 BPS last year to the current 126 BPS, according to Freddie’s numbers.

The ARM share of total applications slipped below 27% from 28% the previous week, according to MBA.