What's the next big trend in selling the American home?

Real estate appraisers are betting it's the pre-listing appraisal posted on the World Wide Web, offering a detailed property description, analysis of up to six comparable houses and professional valuation of the property. It would provide prospective buyers with hard data about a house upfront, before they apply for a mortgage.

Traditionally, professional real estate appraisers have worked for lenders, although their fees are paid by home buyers. Lenders use their data, typically set out in a Fannie Mae-Freddie Mac Uniform Residential Appraisal Report (URAR), to determine how much they can safely lend against a property.

Now appraisers see an entirely different focus for their rich lode of home valuation data: home sellers who want professional guidance, independent of realty agents, on how to price their house to sell for the maximum amount within a specific time period.

Once the pre-listing appraisal is completed, it can be turned into a marketing tool by posting it on the Internet--on a realty agent's Web site, on a for-sale-by-owner Web site or on specialized sites designed for pre-appraised homes.

The Chicago-based Appraisal Institute, a national trade organization that represents 20,000 licensed real estate appraisers, is developing a Web site that will offer such services to home sellers nationwide. A potential buyer, for example, could visit the site, to be called www.OLA.com, for On-Line Appriaisal, and obtain more information on a listed house than is available anywhere. Even the most popular Web sites for home shoppers--www.Realtor.com and HomeAdvisor.com--do not provide the wealth of physical and market data about individual properties that a professional URAR appraisal can supply.

That's because appraisals have almost never been part of marketing houses. But in the Internet age, when smart consumers are demanding that quality information be available free of charge at any hour of the day--professional online appraisals appear to be a natural.

Take the experience of John W. Ross, who recently sold his house in Denver to move to suburban Chicago, where he now is executive vice president of the Appraisal Institute. Like most sellers, Ross and his wife interviewed numerous local realty agents before deciding to list with one. Most agents suggested he list the house in the $187,000 to $195,000 range, Ross said.

Uncertain of where to price it, the Rosses decided to get a pre-listing appraisal--to show to real estate agents and, ultimately, to prospective buyers. After examining the property in detail and researching comparable houses in the area that had sold within the past few months, the appraiser suggested a listing price of $205,000 if the Rosses wanted to sell within 60 days, and $204,000 if they wanted to sell within 45 days.

The Rosses showed the appraisal to the real estate agent they selected and listed the house for $204,000. It sold quickly for "a little over $201,000," Ross said. The appraiser's work "basically put as much as an extra $14,000 in our pocket," Ross said. The cost of the pre-listing appraisal: $325.

Under the Appraisal Institute's forthcoming OLA.com initiative, appraisers conducting pre-listing valuations will post them on that Web site, hot-linking to any other sites the sellers or the sellers' real estate agent cares to use. The OLA.com site will present the house through conventional and virtual-tour exterior and interior photography, and will present the full URAR appraisal for all visitors to see.

The URAR contains virtually every scrap of information needed to evaluate a house: square footage, room plans, lot description, property taxes and assessment, commentary about physical condition of all major features and structural items, plus detailed analysis of comparable houses sold in the immediate market area.

After a national test involving about 300 appraisers starting the first week in November and lasting until March, OLA.com will open its doors to all sellers, buyers, brokers and house shoppers anywhere in the country. Participating appraisers know their work will be on full public display and available to state licensing regulators; Ross is counting on that to produce high-quality, accurate and defensible valuations.

A prototype appraisal Web site--run by Red Planet LLC, the company that is designing OLA.com--is already online and can be visited at www.MFHB.com. The site carries the listings and URAR appraisals of Don Moore, an Appraisal Institute member in Wisconsin. Once the national OLA.com site is up and running next spring, sellers will be able to order appraisals by institute members, then direct buyers to check out their property in unprecedented detail.

Will buyers have to get new appraisals when they apply for a mortgage? They shouldn't in many instances, thereby cutting their acquisition costs by $300 to $400, unless they choose to split the expense with the seller.