How does a major tract of real estate find its way into the ownership of a major developer? In the case of the big Pentagon City tract just across the 14th Street bridge, it was purchased back in 1946 by the late Morris Cafritz and Charles H. Tompkins after Mr. Cafritz had made a trip into Virginia looking at several available sites. The story is that a land broker showed several properties, the last of which was the 200-acre site opposite the Pentagon Mr. Cafritz was generally unimpressed until he returned to his downtown office from the latter site and realized that it had been only a 10-minute drive. WIth that intuitive recognition of "location," he called his friend. Mr. Tompkins, and they eventually made the deal. The remainder of the site now is being developed by Rose Associates of New York City.

If the sale of the YWCA building at the northeast corner of 17th and K streets NW is ever consummated for the $6.4 million bid price, it will mark a new high in downtown - about $350 a square foot.

Maybe you've noticed that the long-undeveloped triangular site at 16th Street and Arkansas Avenue NW has been cleared. That's because the owner, Green Manor Corp., based in Chevy Chase, bought the sloping site from Joseph Bonnett and is starting nine brick town houses that will be priced from $110,000 to $135,000. Maurice Berk of Green Manor said his son, Anton, is handling the project. The zoning and permits for the 2,000-square-foot, three-level houses are in order, Berk said, but the Fine Art Commission must yet grant approval of brick choices et al because the houses will face strip of parkland. The site also is opposite the Crestwood apartments and the six new single houses that Alan Pollin has completed at 16th and Taylor.

On Jan. 16 developer Stephen G. Yeonas will vacate his already sold, large house at 2616 N. Nelson St., Arlington, and move into a town house in the Forest Hills community developed by Albert G. Van Metre opposite Army-Navy Country Club. Yeonas, who formerly headed the family firm that has built many thousands of houses in this area in the past 30 years, now is on his own. And he and his wife are "empty-nesters," a daughter being married and a son in school in Boston. "We wanted to stay in Arlington County," said the exuberant Yeonas, who will be moving into a neighborhood of attached dwellings now price up to $250,000. Among his neighbors will Van Metre, who has beaten Ted Turner twice in sailing competition this year, plus many retired military officers.

Kenneth A. McLean, staff director of the powerful Senate Committee on Banking, Housing and Urban Affairs, told a recent housing forecast conference here that Congress is working on a new set of housing goals for the decade ending in 1988. He added that no major housing legislation will materialize in 1978 unless there is a sharp downturn in housing starts. So far, prognosticators see 1978 starts ranging from a low of 1.75 million to a high of 2.1 million - or a consensus decline of about 9 per cent from this year's expected total of 1.97 units, which is higher than the forecasts made a year ago.

From MCD Holdings, Inc., the building-development firm headed by Albert Turner, comes a yarn about Robert Merson, who builds MCD town houses. He was watching Monday night football when he got a call that sewage was flowing out of a manhole at the Canterbury Riding subdivision in Howard County. Merson met a plumber at the site and they examined the situation,using flashlights. Suddenly, county police appeared on the scene and demanded an explanation. It seems that someone had informed the police that "two weirdos" were doing strange things with flashlights.

Fairfax County has a new pamplet designed for persons planning to build a house in the county. The yellow pamphlet, available at the seat of government in Fairfax City and at all libraries, traces the steps from the purchase of a lot through the application stage, listing all the requirements. One fact: Nine copies of a certified plat are needed to apply for a building permit. And, if the house is valued at $30,000 or more, the contractor must be registered in the state.

The widow of the late TV anchor newsmen Chet Huntley has listed their seven-room contemporary for sale. It's located in the Big Sky area of Montana. The site is 10 acres and the price is $460,000, according to Previews, Inc., the broker. Oh yes, Mr. Huntley's widow is the former Tippy Stringer, who was a TV weatherperson here in the late 1950s, before her marriage to David Brinkley's former colleague.

The folks out at Rossmoor are convinced that the word-of-mouth recommendations of the residents of the adult community are the best selling tools available. That's one reason why Rossmoor residents qualify for a $100 gift certificate from Neiman-Marcus if a buyer goes to settlement after a initial contact from an owner already in the community opened 12 years ago by the Ross Cortesi organization.

The Washington Metropolitan Chapter of the Community Associations Institute will sponsor a seminar on energy conversation at 7:30 p.m. Monday at the Key Bridge Marriott.