The $8.7 million restoration project on the old Potomac Electric Power Building at the corner of 10th and E streets NW. is completed, and the 194,000 square feet of office space has been leased, according to HTB Inc. Architects.

The renovation of 999 E St. marks the completion of a four-year joint effort between HTB, the American Medical Association, the owner and developer of the building, and Turner Construction Co., the contractor, to put the 56-year-old historic structure into working order.

The building was originally designed by Waddy Wood, an influencial designer in the 1930s, and is typical of the architecture in the Washington's financial district at that time. The building was certified by the D.C Landmark Commission as a historic structure, which qualifies it for an investment-tax credit of 25 percent.

Two tenants share the building. The Department of the Treasury occupies 50,000 square feet and the Federal Elections Commission occupies 88,000 square feet.

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

*Several principals of the Vector Realty Group bought a 40,000-square-foot warehouse on 6th and S. Ball streets in Arlington for $1.6 million from Crowne Associates Limited Partnership.

*The Bank of Virginia leased 40,000 square feet at the American Center Office Complex in Tyson's Corner. The bank is relocating its northern regional office from 1710 Goodridge Dr. in McLean.

*International Business Machines Corp. renewed a 51,952-square-foot lease at 21 Firstfield Rd. in Gaithersburg.

*Merrill Lynch Realty leased 6,500 square feet at 7830 Old Georgetown Rd. in Bethesda from the Allwin Building Corp. for a residential realty office. The lease has an aggregate value of $1.7 million.

*Two tenants have leased space at 1325 G St. NW. for a combined aggregate value of $6.9 million. Neighborhood Investment Corp. leased 28,000 square feet and Chemexec leased 11,221 square feet.

*Institutional Communications Co. Inc., previously located at 6917 Arlington Blvd. in Bethesda, leased 10,621 square feet at Tysons Executive Plaza for its new corporate headquarters.