The Federal Reserve continues to throw cold water on the housing market. Mortgage lenders are worried, too, and executives at homebuilding companies are cashing out stock that’s worth billions of dollars.

And homebuyers in Los Angeles County? They just keep setting new records.

September proved to be another robust month, with the median price soaring 22.8 percent from a year earlier, and sales volume jumping nearly 9 percent, although the number of sales slowed significantly from August.

The median price for a single-family home in L.A. County rose to $528,000 in September nearly $100,000 more than a year earlier and up from $520,000 in August, according to data provided to the Business Journal by HomeData Corp., a Melville, N.Y. firm that tracks existing-home sales nationwide.

Experts, surprised at the strength of the market, are nevertheless seizing on data anecdotal and otherwise that might point to declines in coming months. Besides sales volume, which fell to 8,601 resales from 12,107 in August, the number of homes listed for sale in L.A. County has been rising steadily for several months.

Last week, Angelo Mozilo, chief executive of Calabasas-based Countrywide Financial Corp., told Bloomberg News that he thinks the housing market has peaked. He predicted falling condominium prices and a leveling off of single-family home appreciation levels.

“I have been doing this for 53 years and it seems we’re at a level where we’re topping out,” Mozilo said.

The California Association of Realtors’ Unsold Inventory Index rose to 2.7 in August from a low of 1.8 in March. Still, inventories are historically low and well below the 5.7 of August 2004.

With more homes on the market, price appreciation and sales volume typically flatten. Indeed, Leslie Appleton-Young, CAR’s chief economist, said real estate agents are telling her that business has been cooling off.

“I’m hearing anecdotally that properties are staying on the market longer,” she said. “But it’s been all anecdotal, and for whatever reason, it’s not showing up in our numbers yet.”

The strong September results, representing escrows opened mostly in August, have flummoxed housing experts. Many were expecting half the appreciation amount and fewer transactions than a year ago.

Alan Long, president of the Southern California division of Cendant Corp.-owned Sotheby’s International, said that with interest rates hovering near where they were a year ago, he hadn’t anticipated strong sales.

“Knowing that prices and interest rates are higher, that should slow things down,” he said. “But here we have prices and transactions up. I’m a little surprised.”

September marks the third consecutive month of year-over-year home appreciation levels above 20 percent. Except for May and June, year-to-year price comparisons for each month have been above 20 percent.

At 22.8 percent, September’s year-to-year rise was the highest since January, when prices jumped 23.1 percent.

While L.A.’s housing market continues to sizzle, several markets throughout the state are returning to more traditional appreciation rates and sales volumes.

In the second quarter, seven California cities ranked among the nation’s top 20 for home price appreciation, down from 14 in the first quarter, according to a report by the Federal Deposit Insurance Corp.

Meanwhile, the California Housing Affordability Index, a monthly measure of home affordability based on prices, income and mortgage rates, among other costs, showed that 12 percent of Los Angeles households could afford to purchase a median-priced home in August, down from 17 percent a year earlier.

With fewer buyers able to afford the region’s high prices, homes will sit on the market until sellers are willing to accept lower prices. That transition usually takes several months, although Appleton-Young said she is already seeing evidence that seller expectations are lowering.

“Lately, I’ve seen more listings advertising price reductions than I have seen in quite some time,” she said. “It’s not like the sky is falling. The properties were probably priced above the market.”

Long believes it could be a mistake to read weakness into the rising number of listings. More sellers today are overpricing their homes to test how much buyers are willing to pay.

“There are two kinds of homes on the market right now,” Long said. “The well-priced homes move and the overpriced homes languish.”

A big factor in the housing boom has been hybrid mortgages with low introductory interest rates and loans that offer interest-only payments for a number of years. These products have allowed people to buy homes worth more than they could afford otherwise.

Though starter homes on the Westside are topping $1 million, the loans have allowed many buyers to afford the monthly payments.

The latest twist: a 30-year mortgage with 15 years of interest-only payments and no pre-payment penalty. Under that scenario, the monthly payment for a $1 million home is about $4,700 a month. After deducting federal tax breaks, the payment is closer to $3,200.

If borrowers start defaulting, the secondary market private investors as well as Fannie Mae and Freddie Mac won’t continue to buy up the mortgages.