Think it's hard to find a house to buy now? Next week, it may look even harder.

Starting Tuesday, July 31, the inventory of homes for sale will appear almost 50 percent smaller thanks to a major change in the way MetroList, the region's official multiple listing service, categorizes active short sales with contingencies.

In a short sale, a lender agrees to take less than what a borrower owes on a mortgage. Once rare, short sales have become a major part of the post-bust real estate market.

An active short sale with contingency means a would-be buyer has submitted an offer that a lender is considering. Those listings, designated "ASC" on MetroList, have traditionally been classified as active sales but soon will be lumped in with pending sales.

The reason: Lenders generally don't want to receive additional offers on ASCs, said Tom Beede, president and CEO of Metrolist.

"We've been showing properties as active that turn out to be pending sales," he said. "The message here," is that the number of properties for sale is only about "half of what it appears to be."

MetroList denoted 12,248 residential properties in active-sale status this week, including 5,921 active short sales with contingencies.

All will be moved to a new status currently dubbed PSLA for "pending short lender approval," Beede said.

Agents who want to attract additional offers can move a property back to active status, but Beede said he expects that will happen with only about 2 percent of properties.

The new number of active listings will better reflect the true state of the market in Sacramento, El Dorado, Placer and Yolo counties, he said.

Housing inventory is so tight in the Sacramento region that the number of available homes for sale has dropped below the number of pending sales for the first time that Beede, a real estate veteran, could remember.

"For the last four months – April, May, June and July – the number of properties classified as pending sales, meaning escrow has opened, has been greater than active listings on the market," Beede said. "In my 35 years in the business that has never occurred, even for one month."

Real estate agents consider a housing market healthy when it has about a six-month supply of inventory – meaning it would take six months to sell all listed homes. The Sacramento region has had less than a 30-day supply of inventory for months, Beede said.

Such tight inventory can lead only to upward pressure on prices as demand outpaces supply, he said. "We've moved from a buyer's market to a seller's market," Beede said. "I think there's an opportunity for a jump in prices."

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