Spaulding & Slye and International Business Machines Corp. have announced the formation of a joint venture partnership to develop Shady Grove Executive Center, an office park at the intersection of I-270 and Shady Grove Road in Rockville.

The $125 million Shady Grove Executive project, which meets Montgomery County's master plan, calls for phased construction of seven office buildings on 35 of the park's 45 acres.

The complex's projected 1 million square feet include an existing 109,000-square-foot building leased entirely by IBM.

Spaulding & Slye is the managing general partner, as well as the general contractor, exclusive leasing agent and property manager.

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

*Inco Inc., govermment consultants, has leased 95,311 square feet of office space at 8201 Old Courthouse Rd., McLean, from the 8201 Corp.

Coldwell Banker agents handled the transaction, which totaled $18.8 million.

*The Peter N. G. Schwartz Cos. of Washington has been granted a permit by the City of Alexandria to build an office building, called Harbor Center, along the Potomac River in Old Town, at 211 N. Union St.

The 60,000-square-foot, three-story building will have retail space on the ground level and will include a public pier for docking boats.

The architect for Harbor Center is Architects Group Practice of Alexandria. Completion is expected in spring 1986.

-- Fraser Jones