STSC Inc., a Bethesda-based computer-services and software firm, has named Spaulding & Slye to be property manager for a 138,000-square-foot headquarters building being constructed in Rockville.

The six-story structure on Executive Boulevard will be ready for occupancy in November. About 38,000 square feet will be sublet through Spaulding & Slye, a Boston firm with five branch offices, including one in suburban Maryland.

In downtown Washington, the National Association of Realtors has sold its former Washington headquarters building at 925 15th St. NW for $2.75 million to the National Council of Senior Citizens and its affiliated Senior Citizens' Education and Research Center, now operating in the Investment Building.

NAR recently moved its Washington offices into the 13-story Wyatt Building at 711 14th St. NW., which it purchased nearly two years ago for $8 million.

In addition:

Alden Inc. Realtors announced the sale of the former Rock Creek Ginger Ale bottling plant at 500 Penn St. NE for $1.7 million to M&J Associates, represented by M. Max Leder. The two-story brick structure is expected to be remodeled into office space for lease.

Barnes, Morris & Pardoe announced that General Electric Information Services Co. has leased 20,000 square feet of office space at 1300 N. 17th St., Arlington. The total value of the lease exceeds $1.4 million.

The same firm also reported that the 290,000-square-foot building at 1110 Vermont Ave. NW now is fully leased. Recent tenants include Interactive Data Corp. (a division of Chase Manhattan Bank) and the Seattle-based law firm of Perkins, Coie, Stone, Olsen and Williams.

Blake Construction Co. reported it has renovated and leased a former carriage house at 1144 18th St. NW.

The Braedon Companies reported that the Metroplex I building at Landover now is 95 percent leased. New tenants include General Software Corp., Physicians Data Systems Inc. and others. Ground has been broken for the 185,000-square-foot Metroplex II, scheduled for completion next year.

Case Construction Co., a 20-year-old firm at 5135 MacArthur Blvd., has changed its name to Case Design/Remodeling Inc. The firm headed by Frederic F. Case has seven designers who plan extensive remodeling projects.