IN THE BUSINESS . . . Ballantrae Farm, one of the last large estates in McLean, has been sold to the Northern Virginia Land Co., which plans to cut it up into home sites. Northern Virginia Land, which bought the property from the family of Joseph H. Rosenbaum, plans 31 houses on the 32-acre tract, and Mr. and Mrs. Dwight Schar of NVLC will occupy the manor house, which is to be refurbished. The mansion was built in 1928 by Frank Lyon, developer of Lyon Village in Arlington . . . The Calvert Co. Inc. plans to start construction in late summer on the first of 171 new town houses in Lake Ridge, the 3,500-acre planned community on Lake Occoquan. The project, to be known as Peabody Square, will be built in three phases, the first to contain 61 three-level homes of 1,050 to 2,100 square feet priced from the low $80,000s . . . The Patt Organization has announced plans for a 97-unit, shore-front condominium project in Ocean City to be known as The Rainbow . . . Shannon & Luchs has begun to issue a free monthly guide listing more than 300 properties for sale in this area . . . Spaulding & Slye has opened a new office in Northern Virginia near Tysons Corner. The new office will emphasize the marketing of commercial office space . . . Developer W. F. Chesley has begun construction on Greenbelt Medical Office Park in Greenbelt. The 36,000-square-foot building is scheduled for completion in February or March . . . The Community Associations Institute is planning its annual national conference on community associations Oct. 6 to 10 at the Mayflower. PERSONNEL FILE . . .

Rosebeth Realty Corp., which is handling the conversion of The Promenade to cooperative, has named David McFall as the building's manager. Rosebeth notes that more than half of The Promenade's 1,071 units have been sold . . . The Century 21 Brokers Council for Northern Virginia has elected Renee Miller president for 1983-84. Ron Marraccini was chosen vice president; Eddie Huneidi, treasurer; and John Martin, secretary . . . Spaulding & Slye has selected Randall W. Byrnes, senior vice president and Washington regional manager, to be a partner in the firm . . . George H. Beuchert has joined Mulligan/Griffin & Associates Inc. as development manager and associate . . . Herbert F. Collins of Boston has been reelected president of the Council for Rural Housing and Development . . . Randolph Williams Inc. has appointed Sandy Sampson marketing director . . . Keyes Condon Florance Architects has promoted four employes to associates. They are: John Blackburn, David King, Bruce Dicker, and Ron Stup . . . The Gulledge Corp. has promoted Michael F. Rubin to vice president-investment finance and Nanci Porten James to assistant vice president-acquisitions . . . Charles E. Smith Management Inc. has promoted Charles M. Anoff and Barry A. Lewis to assistant vice president, commercial management . . . Long & Foster Realtors has named Peggy Gallagher sales manager of the firm's Columbia branch. ON THE MOVE . . .

American Telephone & Telegraph Co. plans to relocate three new marketing divisions in the Linpro Park office complex in Reston. The move will bring 525 employes to Reston at first, with the number rising to 800 next year. At the same time, AT&T also is planning to establish an office center at North Park, a new 28-acre commercial development in Cockeysville. The company has signed a lease for 42,000 square feet there. Initial employment will total 85. North Park is being done by Park Center Associates, whose managing partners are Jonathan W. Kolker and Jerold C. Hoffberger.