NVHomes of McLean has taken an unusual step to get more of the so-called move-up real estate market in suburban Washington: It has started accepting older homes as trade-ins on new ones.

The Virginia company, which is one of the region's fastest growing home builders, said it will guarantee buyers of new homes in the Maryland and Virginia suburbs that they will get 95 percent of what all parties can agree upon as a fair market price for the existing house, minus the cost of selling it.

Company officials said those costs will total about 11 percent, a figure including a generally accepted 6 percent real estate commission, discount points and closing costs.

As a result, home sellers may find the program more of a convenience in having someone else worry about selling a house than financially advantageous. But James J. Martell, NVHomes' vice president of finance, said the 11 percent figure is equal to what a seller would spend if he used a real estate agent to sell his house.

The cost of financing the trade-in program initially will be covered by fees paid by NVHomes to a new sister company -- NVRealty -- that will operate the program, according to Martell.

But NVRealty will not be a traditional real estate firm. "We are not in the business of buying houses and reselling them," according to NVHomes' President Dwight Schar.

Real estate agents said amenities and marketing programs have to be designed to attract move-up home buyers, whom they describe as among the hardest to lure, because they usually already have a house that is comfortable.

Schar said he believes that he can attract at least one additional sale in each of his developments each month by instituting the trade-in program.

His company ranked as the second-largest home builder in Fairfax County during the first half of this year, according to figures supplied by Rufus S. Lusk & Son Inc., a Washington-based real estate reporting firm.

But Schar and Martell said they are after a bigger chunk of the market.

Taking trade-ins has been tried in other parts of the country, according to William Ellingsworth of the National Association of Home Builders, but the practice is not common.

Sam Finz, chief executive officer of the Northern Virginia Builders Association, said, "I have not heard of any other local builder" using such a program.

Several agents and brokers who do not work for NVHomes said the trade-in program sounded good to them, especially because agents selling an NVHome through the plan still would be guaranteed the traditional 3 percent commission they otherwise would get. Several, however, cautioned buyers to read all the fine print in any contract.

Martell said not all houses will be considered acceptable in the trade-in program. "We are looking for houses that will sell," he said.

Ruth Romano of NVRealty said either the new-home buyer's sales agent or another agent familiar with the area where the existing house is situated and an NVHomes official will work with the owner of the existing house to set the fair market value for the property. In some cases, a third appraiser's opinion may be sought.

After the price is agreed upon, NVHomes will guarantee to pay the buyer of the new house 95 percent of the fair market value of the older house minus the 11 percent.

However, the homeowner is free to market the property at any price he wants to for 30 days. If the house sells for the higher price, the seller gets all the extra money, Schar said.

"At the end of 30 days, the listed price of the house is reduced by one-half of the difference in the original listing price chosen by the owner and the previously-agreed-upon fair market value. At the end of 60 days, the listing price is reduced to the previously-agreed-upon fair market price," Martell said.

"At the end of 90 days, we reduce it even further," he said. Schar said there is a risk that he will be saddled with houses that don't sell. But that is a risk he said he can take because the potential for increased sales far exceeds the risk.