The National Capital Planning Commission, clearing a major obstacle to the Virginia Center for Innovative Technology's plans to build an office complex near Dulles International Airport, yesterday granted the center access to a major highway.

The commission's unanimous decision authorizes CIT and developers of two adjacent properties to build a four-lane highway from their projects to Rte. 28. Without access rights to the highway, also called Sully Road, construction of the 150,000-square-foot CIT complex could have been delayed indefinitely, according to Virginia officials.

The CIT site is located at the intersection of the Dulles Access Road and Rte. 28, on the Fairfax-Loudoun county border. The commission's approval was needed because part of the proposed road would be on the outer edges of the federal airport's property.

"This approval was crucial to our development plans," said William E. Donnelly, a lawyer representing CIT, a state-sponsored research center established to encourage research at Virginia colleges and lure high-tech industry to the state.

The state also could have risked losing the property for the CIT site, which was donated by developers Samir Kawar and Alan I. Kay on the condition that the state win access rights to Rte. 28. Without the roadway approval, the two private developers also would have been forced to significantly reduce their own development plans.

The planning commission in March postponed a decision on the access road until the state and private developers provided additional information on traffic impact. Some commission members expressed concern that the road, whose cost is unknown, would create too much congestion, impeding access to Dulles.

In granting access rights yesterday, the commission recommended that the three developers build no more than one-fifth of their proposed office space until other road improvements are completed in the area. CIT officials and the two private developers say they plan eventually to build 5.2 million square feet of office space on the sites.

The CIT complex would include two buildings for the center's offices and an adjacent building to accommodate a consortium of computer software firms. The two private developers have proposed building hotels, offices and light industrial projects.

Donnelly said that CIT hopes to begin construction on its complex by fall and finish it within two years.