The George Hyman Construction Co. said last week it has completed construction of the French Chancery at 3905 Reservoir Rd. NW, opposite the Georgetown University Medical Center.

Begun in June 1982, the chancery is a 325,000-square-foot complex covering three acres of a 7 1/2-acre wooded site. In addition to offices for the French diplomatic staff, the building houses a 247-seat auditorium and a 379-car garage.

Andre' Remondet, of Paris, is the architect, while RTKL Associates Inc., of Baltimore, is the consulting architect/engineer.

Chevy Chase Savings & Loan has located its newest branch at Magruder House, a two-story brick building dating back to the Revolutionary War. The building recently was restored by the savings and loan to its original appearance.

Magruder House, also known as Locust Grove, was built by Samuel Wade Magruder, a Montgomery County citizen and colonial patriot, sometime between 1773 and 1781. The building is believed to be one of Montgomery County's oldest structures, and one of the few 18th-century buildings in the area.

To celebrate the restoration of the building, the branch's staff will dress in colonial costume during the first month of business, and an exhibit outlining the history of the house and its restoration will be on display.

Magruder House is located at 7340 Westlake Ter., Bethesda, across from Montgomery Mall.

Other recent developments in commercial realty in metropolitan Washington:

* Four Fairfax County offices will relocate to the new Fair Oaks Corporate Center on Route 50, the developer, Rouse & Associates, announced. The Department of Recreation, the Office for Children, the Department of Extension and Continuing Education and the Area Agency on Aging -- employing a total of 125 county workers -- together will occupy a 33,915-square-foot building at the intersection of Waples Mill Road and Pender Drive.

* Greenwell Goetz Architects and Benson, Stein & Braunstein have leased 2,632 square feet and 4,185 square feet, respectively, at 1333 H St. NW.

* United Telecom Communications Inc. has leased 3,171 square feet at 1825 I St. NW from the National Council on Synthetic Fuels Production.