IN THE BUSINESS . . . President Reagan has declared the week of Oct. 2 as National Housing Week, saying "the resurgence of America's housing industry is both a contribution to and a result of our nation's economic recovery." He added that the gain in the number of housing starts in 1983 has restored and created thousands of jobs and "has been a major factor in the reduction of unemployment." . . . Construction has started on Three Flint Hill, the third of five phases in the 48-acre Flint Hill Office Park. The eight-story, 165,000-square-foot building is being developed by the Lerner Cos. and Mar Kap Enterprises. Leasing is by Julien J. Studley . . . Taylor Canfield Associates of Vienna has been chosen to head the marketing drive for Stafford Meadows, the first town house condominiums in Stafford County. Prices in the 152-unit project range from the high $40,000s to high $50,000s . . . Castro Holdsworth Associates is opening models of its new Citation home at a number of locations in Maryland and Virginia. The house features hundreds of options, allowing a buyer to customize his home while paying a production home price, the builders say. . . . DRG Ventures Inc. has purchased Fort Bennett Apartments in Rosslyn for $7.2 million from Fort Bennett Associates. The new owners say they intend to make improvements in the 264-unit garden complex and run it as a rental . . . Era-Tatum Properties reports that its sales volume for its five Northern Virginia offices exceeded $100 million for the 12 months ending July 31. It was the best year in the company's history . . . The Realinvest Group of Washington has named Jones Lang Wootton as exclusive leasing agent for 1726 M St. NW, an 11-story building with 77,000 square feet of rentable space . . . Washington Corp. has formed a wholly owned subsidiary called Sedgwick Properties Inc. to syndicate income-producing real estate. The new firm will concentrate initially on acquiring properties in the Washington area in the $2 million to $10 million range.

PERSONNEL FILE . . . The National Corporation for Housing Partnerships has announced the appointment of two vice presidents: James O. Reich, to be VP-development, and Anthony J. D'Ermes, to be VP-human resources . . . Coldwell Banker Routh Robbins Realtors has named Tom Harwood nanager of the firm's new real estate centers to be opened this fall in six Sears, Roebuck and Co. stores . . . Century 21 of the Mid-Atlantic States has named Edward M. Northrop director for corporate development and Henry C. (Hank) Howells district director . . . Keith A. Taylor has joined Mason Hirst Cos. of Annandale as director of marketing for the firm's commercial development activities, and John G. Doggett has been named director of construction at the firm.

ON THE MOVE . . . 195 Broadway Corp., an AT&T subsidiary, has sublet 70,085 square feet at 2101 L St. NW from the American Petroleum Institute. 195 Broadway will assign the lease to the newly created Central Services Organization after the Jan. 1 AT&T divestiture. Cushman & Wakefield represents the lessee.