Mortgage rates this summer are the best buy ever, according to mortgage company Freddie Mac.

The average rate for a 30-year fixed-rate mortgage was 4.56 percent during the week ended July 23. Moreover, according to the records Freddie Mac has kept since 1971, the rate has hit a new low every week since June 24. After checking other sources, the company says these are the lowest in at least 50 years.

Fannie Mae, another mortgage firm, reported that loans backed by the Federal Housing Administration and the Veterans Administration averaged 4.85 percent.

Buyers have to be asking how much lower the rates can go and how long before they begin to rise to more traditional levels.

" 'How long' is a crystal ball question," said Alex Lieb, operations manager of Access Capital Mortgage in Bethesda, an affiliate of Presidential Bank -- but he doesn't see any dramatic increase taking place before the end of 2011.

Freddie Mac's agrees. Its July Economic and Housing Market Outlook projects the average 30-year rate for the remainder of the year will stay near 4.8 percent and will still be the mid-5 percent range through the end of next year.

"The decline in mortgage rates over the past few weeks echoes the recent signs of weakening confidence in the strength of the economy, particularly the housing and consumer sectors," said Frank E. Nothaft, Freddie Mac's chief economist. "For example, home builder confidence declined in July to lows not seen since April 2009, as measured by the [National Association of Home Builders]/Wells Fargo Housing Market Index, following the large drop in housing starts reported for June."

So are buyers scrambling to take advantage of the rates? The answer is complex.

John Sullivan, an exclusive buyer's agent with Buyer's Edge Inc., also in Bethesda, said business has "fallen off a cliff" in recent weeks. The homebuyers' tax credit effectively moved planned purchases forward from the traditional spring and summer markets, while actual and proposed changes to FHA insurance premiums and the allowable level of seller contributions are offsetting some of the effects of lower rates.

The real problem, however, Sullivan said, is a pervasive uncertainty.

"Buyers feel that prices have not finished falling," he said, "and are afraid they could be underwater as soon as they close. The media has done a good job publicizing the low rates, but there is so much else going on, it gets lost in the noise."

Lieb, however, says low rates are having a positive effect. "Some people who didn't even have buying on their radar are suddenly deciding the time is right." And the salutary effect, he suggests, goes much further than the housing market.

"People, whether buying or refinancing, are getting lower housing costs than they had or expected to have. That is real money in their pocket," Lieb said. "Some people are going to save or pay down debt, but lots of people are going to spend the money, and that is going to help everyone."

One has to wonder, however, if buyers have become too used to continued low rates. The last time Freddie Mac reported a rate over 5.99 percent was the week ended Nov. 20, 2008.

Complacency could be a problem down the road when rates do start to increase, Lieb said.

"It will be hard to convince buyers that 5 percent mortgages aren't coming back when 6 percent becomes the new reality."