The Fairfax County Board of Supervisors decided this week to drop part of a site known as the Chiles tract from further consideration as a possible future location for the county government headquarters.

The board, which since November has been considering moving government headquarters from its present location in the middle of Fairfax City, decided not to consider the southeast quadrant of the Chiles tract, partly because of "enormous traffic problems that would be too expensive to correct," according to Supervisor Martha Pennino (D-Centreville).

The site's planned residential use was another factor that figured in the board decision. The county is relying on high-density commercial growth around any new government site to raise new tax dollars. The Chiles tract is at Rte. 50 and 1-495.

This leaves three sites the board is considering: the Pender site, apparently the number one choice of a citizens committee on relocation, at the southwest corner of the Rte. 50 and West Ox Road; the Smith-Carney site on Rt. 29-211 just south of Rt. 50 and 1-66, and the northeast quadrant of the Chiles tract.

The board appropriated $30,000 this week for an outside consultant to study transportation patterns at the three sites. The board expects to receive Monday the result of commercial appraisals on the three sites.

The southeast section of the Chiles tract was estimated to cost $11 million but recently was purchased by builders Wills and Plank Inc. for $6.9 million to develop single-family homes.

Fred K. Kramer, director of Fairfax County General Services, said the difference between the two figures resulted from a county appraisal based on the commercial value of the site, while Wills and Plank bought it at residential values.