Keeping pace with Ballston's development boom, construction has started on another project in that sprawling suburban minicity: Quincy Street Station.

The mixed-use project is at 4001 N. Fairfax Dr., overlooking Quincy Park. It is bounded by Quincy and Randolph streets, and is one block from the Ballston Metrorail station.

Quincy Street Station will consist of an eight-story, 180,000-square-foot office building and a 10-story, 222-unit residential building. The two buildings will be linked by a half-acre landscaped courtyard.

The John G. Shooshan Co., a relatively new Washington-based firm, is developing the office building. Last week, it sold the residential building to National Development Mid-Atlantic Inc. for an undisclosed amount.

"This will be a good building for a major tenant," said a spokeswoman for Shooshan. She called the Ballston market "extremely strong."

Smith Segreti Tepper McMahon Harned is the architectural firm for the brick-and-limestone building, which will have a green mansard roof. There will be 15,000 square feet of retail space on the ground floor.

Parking for 330 cars will be available. Annual lease rates will range from $24 to $28 a square foot.

Omni Construction Co. is general contractor for the project, which is expected to be completed in 1989.

In other developments in commercial realty:

Computer Based Systems Inc., a computer software company, leased 29,734 square feet at Merrifield Prosperity Business Campus, 2750 Prosperity Ave. in Merrifield, from Trust Co. of the West. Coldwell Banker was the leasing agent.

Dechert Price & Rhoads, a Philadelphia-based law firm, leased 39,471 square feet at 1500 K St. NW from The Oliver Carr Co. Leggat McCall was the leasing agent.

Victor O. Schinnerer Co., an insurance brokerage firm, leased 80,000 square feet in the Chevy Chase Metro Building, 2 Wisconsin Circle, Chevy Chase, from Two Wisconsin Circle Joint Venture. Frank S. Phillips Inc. was the leasing agent.

Announcements of commercial real estate transactions should be sent to Pamela Babcock, Business Department, The Washington Post, 1150 15th St. NW, Washington, D.C. 20071. Information must be received by the Monday prior to publication in order to be considered for publication.