Construction is scheduled to start next April on a $70 million to $80 million corporate office center on a 35 1/2-acre tract near the Tysons Corner shopping center.

Named Westwood, the 900,000-square-foot complex will be built by the Henry A. Long Co., a Fairfax real estate and development firm headed by a former partner of the Long & Foster real estate company.

Long's firm has acquired the property, at 8549 Leesburg Pike (Rte. 7), adjacent to the Dulles airport access highway. It was formerly known as the Dardin estate. The rolling, half-wooded acreage includes a stream across the back boundary. The Long company says its project will be "sensitive to the natural characteristics of the land."

On a smaller lot that also fronts on Rte. 7 next to the Long property, a separate developer (SRS Properties) has proposed a 21-story, convention-style Sheraton Motor Lodge. Although the Long property already is zoned for commercial development, Fairfax County agencies still must act on the hotel project, including a zoning exception to permit the unusually high main tower; (the maximum permitted by zoning is 12 stories or 590 feet above sea level, whichever is lower, but a 24-story tower has been approved for Reston).

Moore Cadillac's new home on Leesburg Pike is adjacent to the entrance for the new office park.

Long said that space will be available to tenants through lease, joint-venture, purchase of building or building site options. First tenants are expected to move in early in 1982. Several multi-story office towers, restaurants and other office complexes are being designed for the office park by the architectural firm of Leo Daly Corp.