The Henry A. Long Co. of Fairfax has announced plans to build a $2 billion office park along 1,000 acres straddling state Rte. 28, south of Washington Dulles International Airport and north of I-66 in western Fairfax.

The giant tract, to be known as Westfields, could produce as much as 20 million square feet of office space over the 15-year construction life developers predict for completion of the project.

That 20 million-square-foot figure "is larger than the existing office base at Tysons Corner today," explained Dorsey Crocker, director of planning and design for the development firm. The project will "be the largest planned commercial development in Fairfax," he said.

"There is not any other place in the area where you could get 1,000 acres together," Crocker said. The acreage was assembled over the last six months, and included purchases from five different property owners.

"We bought a piece here and a piece there, all from speculators," Crocker explained as he pointed to a general site plan in his office. Those speculators had bought the land in anticipation of the intense growth now beginning to take place along the Rte. 28 corridor. The state's Center for Innovative Technology is to be built north of the site; the Westfields project is less than six miles from the western terminus of the Dulles toll lanes.

Crocker would not reveal the price his firm paid for the land.

"We are not speculators. We are developers," Crocker added.

The project has been dubbed by its developers as "the international corporate center at Dulles." Construction on high-technology office space is expected to begin early next year.

When completed, the project will provide jobs for 40,000 to 50,000 people, Crocker predicted.

Westfields is planned to include "headquarters buildings for international and national corporations, a conference center, buildings especially designed for research and development and areas for warehousing and distribution, as well as restaurants, hotels and related services," Crocker said.

There will be plenty of room for the necessary support services within the site, explained Nancy Fisher Stein, Long's director of marketing.

All the land within the site is zoned for commercial development and all roads have already been approved by the county, Crocker said.

The project includes a major network of roads to accommodate on-site traffic, as well as expansion of existing roads. Crocker cited major improvements to both Rte. 50 and Rte. 28. He predicted the day when Rte. 28 will be a six-lane thoroughfare. Construction of internal roads is set for the spring and are to be paid for the developer.

Even without the expanded lanes on Rte. 28, the tract is considered especially valuable because of its proximity to major east-west roadways. The site is between Rte. 50 and I-66 and near Rte. 29, another major commuter artery.

In addition to attracting potential tenants and employes from both Fairfax and Loudoun, developers are hoping to get their share of what they call the "reverse commuter" -- those who live in the District of Columbia and work in the suburbs.

Stein said that it is now a real lure because a commuter can make the trip from the District to the Westfields area in less than a half hour. In addition, "you are going against the traffic," at rush hour, she explained.

The land is already zoned for commercial development, a factor that increases its value because there will no major zoning battles.

"We may give it a shot at some rezoning in the future that might be healthy from a planner's point of view," Crocker said. Some of the land is zoned I-4 or I-5 on adjacent parcels that might be consolidated for a single office complex. In such a case, "there would be a need for minor changes in zoning and the county's comprehensive land-use plan," Crocker said. But nothing will be proposed that would not be permitted under existing zoning, he said.

The office park, as planned, will be limited primarily to six-story buildings. "We will be directing construction and designing the buildings to attract the top corporate tenants . . . ," Crocker said. There are two large 100-acre sites that the Long Co. hopes to build for use by single tenants seeking a corporate headquarters in the Washington area, a spokesperson said.

The Westfields project will include "a full-fledged hotel and conference center," early in the stages of construction, Crocker said. "The county does not have a conference center that will seat 500, but they will soon," Crocker said. Meanwhile, developers of Tysons II, a 107-acre mixed-use development near Tysons Corner, said they expect a conference center to be part of that project, which also has a 15-year building cycle.

The Westfields project is basically surrounded by natural barriers, including streams, valleys, parks and highways. All of these are advantageous to the developer, Crocker said. "We hope to take one of those large sites and build a complex on it looking out over the natural areas." The stream valley park, known as Flatlick Branch Park, is already protected by county regulations.

Westfields is adjacent to a 330-acre residential development to be built by Kettler and Scott Inc., headed by Robert Kettler. The Fairfax Board of Supervisors approved the residential rezoning, which is just south of Westfields, in September. Kettler's project will be known as Sully Station and will include 1,100 housing units.

The main access to the residential areas will now be through new roads to be built through Westfields office areas.

"It is nice to have good quality residential development going in right alongside our project," Crocker said.

Sully Station also will include a commercial shopping area, adjacent to Westfields, to support its residential population.

Crocker pointed to the accessibility of the site tothe airport, the future Center for Innovation Technology and George Mason University as major factors he expects to enhance the market appeal of the office park.

The Long Co. is currently developing an 11-building office complex on 37 acres, south of the Leesburg Pike and west of Tysons Corner Shopping Center, known as Westwood. That project will have more than 1 million square feet of office, retail and hotel space.

The Long Co. was founded in 1979, after Henry Long sold his half of one of Washington's leading residential real estate firms, Long & Foster, to his partner, P. Wesley Foster Jr. Henry Long then turned to commercial development. The company recently moved to a new corporate headquarters at the Commerce Building on University Drive in Fairfax City.