The Mark Winkler Co., a closely held family real estate company that has been in business in Washington for 60 years, has decided to sell its real estate holdings -- one of the largest portfolios in the area -- to several developers for $2.3 billion.

Duke Realty Corp., an Indianapolis company that owns office buildings in 14 cities across the Midwest and the South, agreed to buy the bulk of the company's 32 commercial office buildings in Northern Virginia. That includes office properties at the mixed-use Mark Center in Alexandria, and the TransDulles Center, an office and industrial park just north of Dulles International Airport, Winkler said yesterday.

Duke, which has been looking to expand in the mid-Atlantic since last year, is also buying most of the company's 160 acres of undeveloped land in four Northern Virginia locations.

Winkler agreed to sell most of its residential holdings -- more than 5,000 apartments in 12 Northern Virginia complexes -- to the JBG Investment Fund, an affiliate of Chevy Chase-based developer JBG Cos. The deal will double JBG's residential portfolio.

JBG also plans to purchase the Reston International Center, a 15-story office building on the Dulles Toll Road, additional land by the center, and the right to develop a residential tower on the site. JBG owns the Reston Sheraton and a new development adjacent to the center.

Winkler plans to sell 1801 Pennsylvania Ave. NW, the former MCI headquarters, to an unnamed investor, and 1875 Pennsylvania Ave. NW, which is scheduled to be completed in May, to EastBanc Inc., Winkler's partner in the project. Both buildings will eventually be occupied by law firm Wilmer, Cutler, Pickering Hale & Dorr LLP. That lease, signed in 2003, was the largest private lease transaction in the District's history.

The Winkler Botanical Preserve at the Mark Center is not part of the sale and will continue with an endowment provided by the Winkler family.

The sale of the Winkler family's holdings marks the exit of another family-owned real estate firm from the Washington market. The company's founder, Mark Winkler, ran the business until his death in 1971. Though a daughter, Tori Winkler Thomas, remained the company's chairman, the business was run by outsiders.

Several years ago, the family, led by Mark's window Catherine, now 92, decided to get out of the real estate business and last August began searching for buyers, said Winkler chief executive Randal B. Kell.

"No one was in any hurry. . . . But there were some very good comparable sales in the market that led us to believe we should look at it seriously," Kell said, referring to JBG's move last fall to sell six office buildings to an affiliate of Morgan Stanley Real Estate for $644 million.