IN THE BUSINESS . . . Housing sales dropped 18 percent in April from March's level, but the 3,200 units that were sold still represented a 16 percent jump from the same period a year ago, according to Housing Data Reports. In fact, the sales level reached in April has been exceeded only twice in the past 10 years, HDR notes--March and last October . . . Stanley Martin Communities reports sales of $32 million for the year ended March 31, with the bulk of that--$26 million--coming from residential construction. The firm says it sold 268 houses during the year . . . It being spring, grand openings continue: In Bowie, Fairview, a community of traditional three- and four-bedroom houses at Route 450 and Fairbridge Road. Prices in the project, by Carrollton Development Corp., will range from $129,950 to $144,500. In Alexandria, construction and renovation have begun at Burgess Square, 23 townhouses on a block bounded by South Columbus, Wolfe and South Alfred streets. Six of the townhouses will be new, the remaining 17 restored. Prices in the project, by A&A Partnership, will range from $112,000 to $172,000. In Columbia, Vantage Point, 66 one-, two- and three-bedroom condominiums at Little Patuxent Parkway and Vantage Point Road, opens June 9. Prices range from the upper $50,000s to the $70,000s . . . Maryland Gov. Harry R. Hughes will address the Apartment and Office Building Association's luncheon meeting June 6. For information, call 289-1717 . . . The National Society of Professional Resident Managers will feature D.C. City Councilman H. R. Crawford as speaker at its official installation ceremonies June 10. For information call 429-9440 . . . The Realtors Marketing Institute will offer a six-day course July 11-16 in Springfield on "Fundamentals of Analyzing Real Estate Opportunities." For information call 800--621-7020 . . . Merrill Lynch Realty is offering a series of free seminars for first-time home buyers, Wednesday at the Tysons Marriott, June 11 at the D.C. Marriott and June 15 at the Tysons Marriott. For information, call 530-3200 . . . Century 21 Suburban Properties in Rockville is under new management, its franchise having been taken over by Narinder Singh.

PERSONNEL FILE . . . The Federal National Mortgage Association has named two new vice presidents: Harry Haigley for external communications and A. F. Burfeind for human resources. Haigley has been director of communications with Arthur Andersen & Co. since 1979. Burfeind has been Fannie Mae's vice president for administration and resources since last year . . . Sen. John Tower (R-Tex.), chairman of the Senate housing subcommittee, has named J. French Hill as assistant to the chairman of that subcommittee . . . J. Barry Brown has been named head of Stanley Martin Communities' newly formed commercial division . . . William F. Bittner Jr. of Peach & Co., Inc., Columbia, has been selected for the Howard County Board of Realtors' citizenship award.