A ceremony was held this week to mark the signing of a $70 million lease by Planning Research Corp. for the first building in the new Tyson-McLean Park.

Ten PRC companies with 1,400 employes will consolidate operations next year in the 440,000-square-foot, X-shaped building, which was designed by DI Design and Development of Toronto and built by Omni Construction Co.

The park, which will eventually have two more buildings, is on Lewinsville Road at Dolley Madison Boulevard.

PRC, a diversified professional service organization, moved to this area from Los Angeles two years ago. The firm plans to have more than 2,000 employes in Northern Virginia by 1986.

The developers of Tyson-McLean Park are John T. Hazel, Milton Peterson and Duane W. Beckhorn. A spokesman said that the 15-year lease for the first building is the largest agreed to by a private tenant in this area.

The Tyson-McLean Park buildings will be only six stories high inside a park strip, with an easement for preservation of green space. The first building, which is being constructed in two adjoining sections, will have energy-conservation features including window shading, tinted glazing, revolving entrance doors inside a vestibule and a heat-recovery system for the computer room.