In the depth of the housing bust, so many Fresno-area houses were for sale -- and so few people were buying -- that the Fresno multiple listing service estimated it would take more than a year and a half to sell everything then on the market.

That was 2007. Now, it's a whole different market: So many buyers are shopping for houses -- and so few are for sale -- that the supply of available homes could be sold in as little as four months.

The change has been so dramatic that sellers are getting multiple offers, sometimes within hours of listing a home. And buyers are often paying more than the asking price.

Is this a sign that the housing bust is about to become a boom again?

Maybe not, experts warn.

Although some buyers are finding themselves in a bidding war for well-kept homes in desirable locations, prices overall remain flat.

Foreclosures and short-sales still make up almost half of home sales in Fresno County, according to the Fresno Multiple Listing Service, and the possibility of more foreclosures flooding the market later this year remains a drag on prices.

"It's a highly unusual market," where the short supply appears to defy normal economics, said economist Jeff Michael, director of the Business Forecasting Center at Stockton's University of the Pacific.

Lenders are screening borrowers more carefully, and appraisers are conservative in their appraisals, which keeps prices in check, Michael said.

"But at some point [foreclosures] will diminish and there will be pressure on prices to pick up."

In 2007, there were 6,655 properties listed for sale in Fresno County, according to the Fresno Multiple Listing Service. At the end of 2011, the number was less than half that -- just 2,711.

Agents say that buyers picking up cheap houses have whittled down the inventory. There are also fewer distressed properties for sale as lenders fix them up or work with delinquent homeowners to modify the loan or help them catch up on payments to avoid foreclosure.

Homeowners who have equity are hanging onto their homes until prices inch back up, said Gary Painter, director of research at the Lusk Center for Real Estate at the University of Southern California.

Home prices are unlikely to increase until the job market in areas like Fresno improve, Painter said. The only places that have seen a small improvement statewide are San Francisco and the Silicon Valley, where the job market has been stronger, he said.

Local real estate agents are optimistic about sales, but they are reluctant to call it a recovery. The activity, they say, is a good indication that the real estate market is improving.

"We haven't seen price appreciation yet," said Patrick Connor, president of London Properties in Fresno. "We're bouncing if not at the bottom, near the bottom. I think barring any major economic, fiscal or international disaster, we have to be either very close or at that turning point."

But coaxing homeowners to sell right now is a challenge.

To entice more sellers, Keller Williams Realty of Fresno is holding an unusual Friday afternoon home tour this week. Keller Williams agents will hold 30 open houses in central and northeast Fresno and Clovis from 4 to 6 p.m. Friday.

Besides pulling in potential buyers, the goal is to attract homeowners in those neighborhoods who might be willing to put their homes on the market, said Joanna Odabashian, Keller Williams Realty team leader.

Her pitch to homeowners: Sell and buy a bigger home for almost the same payment as they have now.