Cadillac Fairview Urban Development Inc. this week turned over to Virginia an $18 million expanded interchange on the Capital Beltway at Route 50 in Fairfax -- though the new roadways will not be open to traffic for several months.

The transfer took place at ceremonies in which Cadillac Fairview also released details on the development of its 220-acre Fairview Park office and retail project at the site.

When completed in approximately 10 years, the development will contain 19 buildings, including a 450-room Marriott Hotel that Cadillac Fairview officials said will be "the flagship" of the Marriott chain in the Washington suburbs.

Developers said the new interchange will funnel traffic across Route 50 on a new bridge that is part of a new road to be known as Fairview Park Drive. The system will provide direct access from the Beltway into and out of Fairview Park and is expected to help alleviate traffic jams along the Route 50 corridor near Gallows Road near Merrifield.

The $18 million in road money spent by developers is part of more than $25 million in road improvements promised to Fairfax in exchange for rezoning the land involved from residential to commercial-office-park status, according to attorneys representing Cadillac Fairview.

The 4 million-square-foot development, which will include office, hotel and retail space, is being built in two parts inside and along the Beltway on the northeast and southeast sides of Route 50.

The new interchange will not be open for several months and cannot be accepted into Virginia's state highway system until all parts of the road network in the interchange area meet highway department standards, transportation officials said.

The first tenant in the development will be Computer Sciences Corp. , a California-based high technology company. CSC is a partner with Cadillac Fairview in a joint venture to construct five buildings expected to cost a total of $90 million.

Construction is under way on the first of the five, according to William R. Hoover, president of CSC. The new CSC facility will employ 2,500 people, many of whom already are working for the company in the Washington area.

Hoover predicted that number will jump to more than 5,000 employes "within the next five years."

"CSC is the largest independent supplier of computer-based services to the federal government," Hoover said. Although a major part of CSC's business is with the federal government, Hoover said there are no plans to move corporate headquarters from California to Washington.

Hoover said his company last year won a $282 million contract for the development of an integrated communications network for the Treasury Department. In addition, 30 percent of CSC's contracts with the government are defense-related, Hoover said.

In addition to the CSC building, construction is under way on the centerpiece building of the Fairview Park development. Designed by the architectural firm of WZMH Group Inc., the 14-story, 250,000-square-foot building is in the southeast corner of the Beltway and Route 50.

Fairview Park is a joint venture of Dallas-based Cadillac Fairview Urban Development and Copley Real Estate Advisers, an affiliate of New England Life Insurance Co. Cadillac Fairview Urban Development, itself a subsidiary of a large Canadian firm, is the development partner.

The 19 office buildings planned will contain 3.6 million square feet of space. Another 100,000 square feet of retail space is planned, officials said. The first Cadillac Fairview building and the first CSC building are expected to be finished within the next 18 months.

Cadillac Fairview President Michael Prentiss described the development as a "high-end professional park" that he expects to appeal to banking operations and law firms as well as high technology industries.

Buildings in the giant complex are being planned for what Prentiss called "general-purpose structures built to accommodate most any tenant." Buildings are being designed by several architects rather than one, Cadillac Fairview officials said.

Although the Fairfax County office vacancy rate is hovering near 12 percent, Prentiss said Fairfax is doing quite well compared with other major office markets across the nation.

"The key in real estate today is being close in. Being on the Beltway is a great advantage in leasing," he said.

Developers will keep approximately half of the 220 acres in open, heavily wooded space and will create two lakes of more than 20 acres.

Cadillac Fairview has modified development plans to "include more structured parking, providing more green space" than originally promised, Prentiss said. He said existing trees would provide natural buffers to hide parking garages.

Hoover said that CSC picked the area because it was looking for a place for "major future growth" that provided "easy access to downtown and surrounding suburbs." Hoover said he believes that the area provides the "right environment for hiring the best professionals in the field."