Construction has begun on a 135,000-square-foot office and retail building at the southwest corner of 20th and K streets NW, Farragut Development Co. has announced. The building, with a facade of limestone and granite, will pick up on numerous "architectual themes of older buildings in Washington," and will include several turrets, according to Farragut Development President Ronald A. Goode.

The $26 million project includes 11,000 square feet of retail space, 124,000 square feet of office space, and two levels of underground parking. The architects are Skidmore, Owings and Merrill, with general contracting by Omni Construction Inc. The marketing agent is Cassidy, Jaeger and Pinkard Inc. Construction is scheduled for completion in for the summer of 1986.

The U.S. office of Saab-Fairchild Aircraft Ltd., which is developing and manufacturing the Saab-Fairchild 340 twin turboprop regional airliner and corporate aircraft, plans to relocate this month from a building near Dulles International Airport to headquarters closer to the airport.

The new office is in the corporate center recently built by Fairchild Industries Inc., the U.S. partner in the joint venture with Sweden's Saab-Scania AB since 1980. The new headquarters will house Saab-Fairchild's marketing and finance divisions. Saab-Fairchild also occupies a separate product support facility at Dulles totaling 11,500 square feet.

The Saab-Fairchild 340 is now in operation with six airlines on three continents, including Cincinnati-based Comair and Air Midwest of Wichita, Kan. Since last summer, when the first plane went into service, the company says it has received orders for 65 aircraft from airlines throughout the world.

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

Vitro Corp. plans to develop 24.5 acres at the intersection of West Gude Drive and Route 355 in Rockville, Vitro President has announced Robert C. Gormley.

The John Akridge Co. has announced that its latest project, an 118,000-square-foot office building at 1133 20th St. NW, is 71 percent leased. Major tenants include Northwestern Mutual Life Insurance Co. and the American Association of Retired Persons.

Construction has been completed on a new addition to AT&T Communications Data Center at 12401 Columbia Pike in Silver Spring.