More than two square miles of mostly wooded land dotted with small pockets of residential development around the interchange at I-66 and Rte. 50 in Fairfax County are expected to undergo extensive development soon. A sewer system financed by local landowners is scheduled to be built here within the next 18 months.

Contracts will be let by mid-June on a $1.76 million sewer project that is expected to open up the 1,463 acres around the interchange to residential, commercial and industrial development. The project, to entail two pumpover stations as well as force mains, is being financed by the Route 50-66 Association, a group of 18 landowners in the area, under contract with the county.

The area around the intersection of two of Northern Virginia's major traffic arteries has long been considered prime land for development.On county Planning and Land Use System (PLUS) maps, the county's master plan for development, a regional shopping center is called for west of the interchange, with low-density residential development to the northwest and high-density residential development south of I-66, west of the interchange.Industrial development is planned for the eastern part of the area, adjacent to Fairfax City.

In addition, the County Board of Supervisors is considering relocating the county's government complex outside Fairfax City; two of the three possible sites for the center lie in the "West of Fairfax" area near the interchange.

Recently the Fairfax County Chamber of Commerce in a study to identify possible future employment centers for the county defined the land around the interchange as "prime," said Suzanne Paciuli, who headed the chamber's study commission.

"We said in our report that the Rte. 66 corridor in Fairfax Couty 'could be equivalent to Montgomery County's Rte. 270 corridor,'" said Paciuli.

But the sewer has been the key. Since 1964, landowners in the area have been working together in the Route 50-66 Association, headed by Jack W. Carney, to get the necessary system built. Although the area lies in the Difficult Run Watershed, county planners decided in the late 1960s that to equalize treatment loads, sewage in the interchange area would have to go to the Accotink plant rather than into the Difficult Run system, which runs to the Blue Plains Treatment Plant. That meant building a more complicated system that would pump sewage uphill, through Fairfax City, and on down to Accotink. In 1971, the association landowners entered into contract with the country to finance the system, and in 1973-74, association landowners put up $900,000 to increase the sewer mains in Fairfax City to accomodate the extra sewer flow. Now they plan to finance the remainder of the project.

Association chairman Carney is partowner of the Smith-Carney tract on Rte. 29-211, which is one of the sites being considered by the county for a new government center. Part of another site under consideration - the Pender tract, at the intersection of Rte. 50 and West Ox Road - lies in the area to be sewered. A development plan for Carney's land already has been filed with the county for 1,316 residential units and a neighborhood shopping center. The development will be served by the sewer when it is built.

Installation of the sewer will also serve a 1.3 million-square-foot regional shopping center called Crossroads, where the Pinecrest Golf Course now is located just east of the intersection of West Ox Road and Rte. 50. Taubman Co., developer of the shopping center, plans to break ground for the project in July.

"The interchange area has been planned for a major population center," said county planner Carolyn Manchester, who works specifically on the West of Fairfax area. "We're trying to see that the 'mistakes' made at Tysons are not made here. We don't want to get Rte. 50 so people can't move down it."

The traffic that will be generated by future development is of major concern to the people who live either in or on the periphery of the interchange area.

"We're pretty resigned to the kind of development that is going to occur," said Gretchen Davis, president of the Fairfax Farms Civic Association. "But traffic is already a problem."