The Cambridge House apartment building at 1221 Massachusetts Ave. NW has been sold for $3.45 million to the National Beauty Culturists League Inc., an organization representing beauty shop owners and operators. Financing included an FHA-insured loan under Section 223(f). Dorothy K. Winston acted as the broker in behalf of the selling group, Columbia Realty Venture, headed by Norman Bernstein. In addition to apartments, the building has commercial office spaces.

Potomac Electric Power Co. has asked developer-builders for proposals to enhance the 1 1/4-acre tract on which Pepco has long had a power sub-station at 33d and K streets NW. The Georgetown site is next to the Flour Mill luxury condominium being developed by Marvin Weissberg. A Pepco representative said that the sub-station would remain on the tract but that unused ground would be available for an office or apartment building. An office building at 1919 Pennsylvania Ave. NW is currently being developed by the Quadrangle Corp. around a site that includes a small power station.

Two 16-story condominium apartment buildings are currently under construction on the 100-acre Skyline City complex that the Charles E. Smith Companies is building on a former private airport site at Baileys Crossroads, Two 26-story rental apartment buildings, two 26-story condominium apartment buildings, two 16-story office buildings and shopping and health facilities are also on the site. A mid-section of one of the condominium buildings collapsed during construction in 1973 but the building has since been rebuilt without incident. When completed, Skyline City will have a total of 3,500 apartment units, 2.5 million square feet of office space and a 400-unit motel.

JaLaur Corp., headed by Walter H. Magruder Jr., is completing the final group of 58 single-family houses in Highland Knolls at Damascus, where the firm began selling houses priced below $55,000 a year ago. JaLaur is beginning new detached houses at Spring Ridge Farm in Damascus. Opening prices are expected to be in the $65,000 range, when sales begin later this month.

Builder Allan Pollin is completing a $235,000 contemporary house designed by Wilkes & Faulkner at 2201 N St. NW. Located at the end of a group of existing rowhouses, this contemporary dwelling is being built for Eric Rudd, a young sculptor. The three-story house has a circular stairway and a wall of glass in the dining room.

C. E. Swift has opened a firm called Swift Referrals Inc., 8237 Georgia Ave., Silver Spring, which he said is "testing the water" for operation of an areawide buyer referral service for homes for sale by owners selling their own dwellings or working with discount realty brokers. The fee for owner is $65. Swift said prospective buyers pay no fees and are referred directly to the owners.

Alan Dobson, a carpenter who came to the U.S. from England 10 years ago, is building a house he designed that is made up of five octagon-shaped cubes, one of which is an atrium. A friend, Rod O'Shea, is buying the house, which is on a 24-acre lot in Great Falls at the end of Boyle Lane, overlooking the Potomac. The exterior will have redwood siding in diagonal patterns. Dobson said the lot cost $95,000 and that the four-bedroom, six-bath house will cost the buyer an additional $250,000. CAPTION: Picture, Cambridge House has been sold for $3.45 million.