Despite initial reports that potentially dangerous levels of radon gas were detected at several Fairfax County schools, follow-up testing found no problem, the county School Board was told last night.

Alton Hlavin, an assistant superintendent, assailed what he called misinformation released by the Fairfax County Federation of Teachers on the school system's radon tests at its 178 schools.

Radon is a colorless and odorless radioactive gas produced by the breakdown of uranium deposits in the soil. By seeping into buildings, it can increase to potentially hazardous levels linked to lung cancer if a person is exposed to the gas over many years.

The federation said two schools, Lee High and Belvedere Elementary, had two radon readings above four picocuries per liter of air, a level the Environmental Protection Agency says requires monitoring.

Three other schools, West Springfield Elementary, Thoreau Intermediate and Westgate Elementary, had one reading above four picocuries and were not retested, the federation said in a Sept. 30 news release.

Hlavin said last night that all schools were retested. The later readings were under four picocuries in all cases, he said.

Hlavin said the school system is taking steps to ensure proper ventilation at one school construction site where extremely high levels of radon -- 4,000 picocuries -- were found in the soil. Safe construction methods can eliminate the potential problem at the Hiddenbrook school site in Herndon, he said.

Hlavin said all schools will be tested again at some future date, and special attention will be paid to schools with at least one reading above four picocuries.

School Board members said the report allayed their fears. "We're very pleased that you have been way out front on this issue," said Chairman Mary E. Collier.

In other business, the board adopted a list of hoped-for legislation for the 1988 Virginia General Assembly session that includes two proposed bills to help school officials assure that school employes do not have criminal records, especially child abuse convictions.

One bill, defeated by the legislature last session, would allow nationwide criminal record checks of all job applicants. The other, proposed after a Reston assistant principal was found to have been convicted of criminal charges in Prince William County, would require that neighboring jurisdictions notify each other when school employes are convicted.