An option agreement to buy the multi-million-dollar, 360-acre Washingtonian complex at Shady Grove Road and I-270 in Montgomery County has been acquired by a subsidiary of Mobil Land Development Corp.

A Mobil spokesman said that the four-month option period will be used to study the development feasibility of the property, which includes two golf courses, a 97-room motel and undeveloped land. Development possibilities include residential, varied business and a hotel-conference facility.

Owned by Eig Enterprises, the property has been a landmark in Montgomery County since the 1959s. The veteran builder/developer Samuel Eig and attorney John McKeever have been partners in the enterprise.

Neither Mobil nor Eig spokesmen would divulge a possible price for the property.

McKeever confirmed yesterday that the firm is liquidating its varied holdings. Earlier, the Eig group sold a 26-story apartment building to Ward Development, which has converted it to condominium ownership. The site of the defunct Shady Grove Music Fair theater has been in the process of being sold for redevelopment.

Mobil Land Development Corp., based in New York but with a regional office in Reston, has been developing remaining land in Reston and redeveloping the Colonial Village apartment complex in close-in Arlington.

Mobil's newly formed subsidiary, Washingtonian Land Cory., has signed the option for possible purchase of the Washingtonian property.