Blake Construction Co, will begin work soon on a 10-story office building above Metro Center at 1120 G St. NW, where the Neisner department store once stood. The architectural firm of Mills, Clagett and Wening designed the glass- and brick-faced building, the first new construction above Metro Center at 12th and G streets. The building is to be finished in the fall of 1981.

Commerce Secretary Philip Klutznick and Housing and Urban Development Secretay Moon Landrieu will speak at the 49th annual meeting of the National Housing Conference Monday and Tuesday at the Capital Hilton hotel. Other major speakers include Sen. Harrison Williams (D-N.J.) and Rep. William Moorehead (R-Pa.).

The Northern Virginia Board of Realtors reported that its members sold compared with 1,527 units for a total of $114 million a year earlier.

The Metropolitan Washington Planning and Housing Association will conduct a public forum on the rental market in the city at a luncheon Wednesday at the Empress restaurant. The condominium conversion of the McLean Gardens apartment complex will be discussed. For information, call 737-3700.

A national network of franchised home inspection services called HouseMaster of America Inc. is being organized in Bound Brook, N.J. The chairman is Kenneth T. Austin.

An 11-story building at 1029 Vermont Ave. NW is being remodeled by Vermont Associates, a group that bought the structure recently for more than $950,000 from Perlberg Holding Corp. of New York City.

Helen M. Hubbell has been named regional vice president for central Montgomery County by Colquitt-Caruthers Inc. She has been with the firm since 1972.