Wang Laboratories Inc. of Lowell, Mass., has opened a new headquarters for its federal systems division in the Bethesda Metro Complex at 7500 Old Georgetown Rd.

The division, the computer manufacturer's largest, will occupy nine floors of the newly completed, 16-story office building, and will employ 400.

Constructed by Clark Enterprises Inc. under a limited partnership with Wang, the building is the first to open in the Bethesda Metro Complex.

Gannett Co. Inc., which recently announced plans to relocate its corporate headquarters to Rosslyn, has leased 230,000 square feet in the second of the Twin Towers at 1100 Wilson Blvd.

Beginning in 1986, 250 of Gannett's top officers and managers will move into offices on 11 floors of the 30-story Tower II. The communications firm will occupy a total of about 450,000 square feet in the two curvilinear buildings.

The Twin Towers, the tallest buildings in the Washington area, were originally designed by Hellmuth, Obata and Kassebaum, while the architect for the second building was VVKR Inc.

The developer and owner of the project is Stanley Westreich, a partner in the firm of Westfield Realty.

Other recent developments in commercial realty in the Washington metropolitan area:

Comsearch Inc., a firm specializing in microwave systems and analysis, announced construction has begun on its new headquarters on Sunrise Valley Drive. The 60,000-square-foot, five-story building is a joint venture of Comsearch and Tetra Partnerships, and was designed by the Reston architectural firm Stanmyre & Noel.

Computer Entry Systems Corp., a manufacturer of cash management and payment processing systems, has signed an agreement with the Case/Rixon Corp. to lease a facility in the Montgomery Industrial Park in Silver Spring. CES will lease 11,500 square feet of manufacturing space in the park, and in early 1986 will move its entire operations into a new, 75,000-square-foot facility.

Hecht's has re-opened its Ballston Common store, in the Parkington Shopping Center, after a nine-month, $5 million renovation. The rest of the shopping center is undergoing a $70 million refurbishing.