Two recent entries into Washington's torrid housing development scene are Conrad and Carter Cafritz.

Sons of the late builder-developer Morris Cafritz, they are building moderately priced houses in Prince William County for what Conrad, 39, describes as the "move-up" market.

The development, called the Harbors of NewPort, is taking place on a 1,100-acre tract east of Rte. 1 and south of Neabsco Creek. The entry road, Rte. 610, winds to a marina near the Potomac.

Morris Cafritz, who built more than 10,000 houses in the Washington area before he died in 1964, bought the Prince William land in 1960. He was also the developer of more than two dozen downtown office buildings and area apartment complexes.

Conrad Cafritz, 39, and Carter, 41, who have been working together in varied real estate enterprises and holdings for more than a dozen years, are building single-family houses for the first time.

"Obviously, the area housing market is strong," said Carter, "and we felt that moderately sized single houses with traditional front facades would be right for these wooded lots."

This year the brothers, whose firm is called NewPort Development, Inc., are planning to build 70 houses ranging in price from $59,000 to $76,000. The building pace is expected to be stepped up slightly next year. Models were opened last weekend, with Mount Vernon Realty as the sales agent. Conrad said that four sale deposits were taken and that "traffic was good."

Conrad and Calvin Cafritz said their venture into single-family dwellings was the result of wanting to control the development.

The brothers said they expect the NewPort location, which is 30 miles south of the District, to become even more strategic after a major interchange is created on nearby Rte. 395 in a few years. A regional shopping mall is planned near that interchange.

The Cafritzes plan to develop NewPort into a community of 800 single-family houses, with higher-density town houses and apartments and some commercial development.

Neither brother has a role in the surving Cafritz Co., which handles most of the properties from their father's multimillion-dollar estate. Six years ago, their older brother, Calvin, now 46, left the presidency of the firm to strike out on his own in real estate.

Their mother, Gwendolyn, became president and Martin Atlas took over as executive vice president and chief operating officer. Both continue to serve in those posts.