The following were among actions taken by the Fairfax County Board of Supervisors at its July 27 meeting. For more information, call 691-3187.

SOUTHEAST FAIRFAX DEVELOPMENT CORP. -- The board, ending months of wrangling between citizens and developers over the Southeast Fairfax Development Corp. (SFDC), a private, nonprofit organization established to help revitalize the county's Rte. 1 corridor, voted unanimously to increase the number of citizens on the group's board of directors.

Since its founding in 1982, SFDC has received about $800,000 from the county. But the group has come under fire recently for allegedly conducting meetings in secret, favoring developers, and ignoring suggestions of county residents.

In response to these charges, the board voted to add two additional citizen representatives to the board, bringing the size of the board to 18, and to require SFDC board members to disclose financial ties to developers.The board voted to permit the SFDC to go into private, executive session only for reasons allowed under the Virginia Freedom of Information Act.

The board did not follow a suggestion of some citizen groups that had urged public disclosure of all contributions, voting instead to allow anonymous contributions to the organization to continue.

GOVERNMENT CENTER -- The board ordered County Executive J. Hamilton Lambert to review a proposal to swap county-owned land with a developer in exchange for the developer building a new county government center.

Under the plan currently being considered by the board, the county would trade 116 acres of prime development land near Fair Oaks Mall in exchange for construction of the proposed 633,000- square- foot government center -- estimated to cost $83 million -- by the Charles E. Smith Cos./Artery Organization Partnership.

For years, Fairfax County has considered building a new government center to move county offices from the Massey Building located in Fairfax City. Since the Massey building was completed in 1969, the number of County government offices have vastly outgrown the building and many offices now rent space in Fairfax City.

The board ordered Lambert to compare the land swap with the cost of financing the $83 million project with bonds, a measure that has been supported by the Fairfax County Federation of Citizens Associations. Lambert will also provide an estimate of financing two thirds of the project with bonds, while financing the remaining costs with lump sum payments. Supervisor Thomas M. Davis III (R-Mason) said the additional information was needed for the board and the public to know the alternatives to the land swap. The board will vote on the government center proposal Aug. 3.

RADON TESTING -- The county released the results of its radon testing project, which concludes that the county does not have a major radon problem.

More than two-thirds of the homes surveyed by the county had very low levels of radon while only 2 percent had radon levels that could pose a high risk to residents. About 32 percent of the houses had "borderline" levels of the radioactive gas. The county will test these houses again to double check their radon levels.

Radon is produced by the natural decay of uranium, which is found in almost all soils and rocks. The gas usually seeps into houses through cracks or holes in the foundation, giving off radioactive particles that can lodge in the lungs and damage lung tissue.

The results came from the first year of a two-year project to test 2,400 county homes for radon. The county tested 1,200 homes from December 1986 to February 1987 and will test 1,200 more next year.