Three young Washington area men who are enthusiastically building their seventh small subdivision of single-family houses in Northern Virginia, say they recognize that the market may be frosted by fall. But they say they can weather it.

"We organize PAR Construction Corp. in 1973 and opened our first subdivision (Plantation Estates in the Mount Vernon area) in early 1974," said Gary Rappaport, 28. "And everyone remembers how tough it was to sell houses then. But we have enough mortgage commitments, at 9 1/2 percent, for the rest of this year. That's a plus."

Rappaport's partners are Steven Powell, 30, a third-generation builder who has a degree in biology from Baldwin-Wallace College in Ohio, and Robert Haft, 25, who has Harvard University graduate degrees in business and urban planning. Rappaport is a graduate of Syracuse University, with a major in computer sciences.

"Bob Haft and I are related by marriage. His father, Herbert Haft of Dart Drug, is my father-in-law. Steve Powell and I founded PAR (for Powell and Rappaport) and Bob Haft joined us last fall. He still has an interest in Dart Drug and Crown Books but spends at least two days a week with us on financing and marketing."

Rappaport said he came to Washington "to perform. I didn't want to continue working for my father in the shirt business in New York nor to work for my father-in-law in Washington. After meeting Steve Powell, I realized that we could combine our talents in home building."

As the result of his interest in land acquisitiopn and financing, Rappaport said he keeps tabs on all zoning action and land acquisitions in suburban Virginia. "We want to know where we want to build and who will be building near us," he said.

In the field, Steve Powell works with building subcontractors in what Rappaport described as a "friendly, low-key manner." The firm's newest job is Towlston Meadows in the Great Falls area.

Rappaport said the firm has buyers for all the houses it will complete through September. "We're enough aware of the current market to be aware of the problems that confront speculative builders," he said. "We do not paln to be caught with an inventory of unsold houses."