By Holden Lewis, Bankrate.com

The big economic story continues to be the effects of Hurricane Katrina. Its impact on mortgage rates and real estate will be contradictory and sometimes surprising.

Long-term mortgage rates have been stuck in neutral since the hurricane struck, and a lot of experts don't expect those rates to rise much for the rest of the year. The price of plywood and asphalt roof shingles will go up, though, as homeowners and business owners on the Gulf Coast make repairs. Economists generally believe that rates will rise next year as the economy regains momentum. They expect home values to keep rising and building materials to remain expensive.

The benchmark 30-year fixed-rate mortgage rose 4 basis points to 5.84 percent, according to the Bankrate.com national survey of large lenders. A basis point is one-hundredth of 1 percentage point. The mortgages in this week's survey had an average total of 0.37 discount and origination points. One year ago, the mortgage index was 5.76 percent.

The 15-year fixed-rate mortgage rose 5 basis points to 5.44 percent. The 5/1 adjustable-rate mortgage rose 4 basis points to 5.40 percent.

Observers look at the economy in terms of pre-Katrina and post-Katrina. "Pre-Katrina, the Federal Reserve had implied that it was likely to continue boosting the federal funds target at quarter-point increments," writes Freddie Mac's chief economist, Frank Nothaft, in his September economic outlook. Now it seems likely that the Fed will pause its rate-hike campaign "to assess the fragility of the economy and to support the credit needs of recovery efforts."

The prospect that the Fed might hold rates steady at its next meeting, scheduled for Sept. 20, has kept long-term interest rates in check, Nothaft says. He thinks the average rate on a 30-year fixed will remain below 6 percent "for the balance of the year," then rise next year.

That's how Bob Moulton, president of Americana Mortgage Group in Manhasset, N.Y., sees it. "The U.S. economy is pretty resilient," he says. "I think we'll bounce back." Trying to guess at the timing, he says it took four to six months to rebound from the terrorist attacks of Sept. 11, 2001. It's anyone's guess whether this initial recovery stage will happen any faster.

Moulton believes rates will rise next year, maybe to 6.25 percent or 6.5 percent. Modestly higher rates won't put much of a dent in home prices, Moulton predicts -- but if heating costs skyrocket while mortgage rates rise, "that could start to affect first-time home buyers."

He had clients, in February, who asked to delay the closing on their house, because they didn't want to pay heating bills in the dead of winter. If people do that in large numbers this coming winter, home prices could suffer.

Katrina led to a spike in fuel prices, and most observers expect fuel prices to drop as the Gulf's oil production, refining and shipping industries recover. But an unusually cold winter could cause prices of natural gas and heating oil to rise, and that, in turn, could slow economic growth and keep interest rates down.

So no matter what, weather will affect mortgage rates and even home values.

By the time the construction season heats up next spring, increased demand could bring higher prices for lumber, cement, gypsum board and other materials, Nothaft says.

The economists at the National Association of Home Builders aren't so sure that demand for building materials will rise dramatically next spring. Past disasters, such as Hurricanes Andrew and Hugo, didn't result in a massive surge in home building, the NAHB says. Reconstruction happened gradually.