The state agency that regulates worker safety is closing its investigation of naturally occurring asbestos in Fairfax County after an inspection of one construction site found no health threat, a state official said yesterday.

Inspectors determined that the level of airborne asbestos fibers at the Fair Oaks Commerce Center site near Fair Oaks Mall was within safety limits, according to Clarence Wheeling, the health enforcement officer for the Virginia Department of Labor and Industry. When inhaled in large amounts over an extended period, asbestos can cause cancer.

Naturally occurring asbestos was identified in rock samples taken from more than two dozen locations throughout the county, but inspectors checked only the office building site because it was referred by the Environmental Protection Agency, Wheeling said.

His office needed a referral from a government agency or a complaint from an employe to investigate further, Wheeling said.

"We haven't gotten any complaints" on the other sites, he said. "If precautions are followed, there is no reason to believe there is a hazard in the others."

The agency's decision is likely to be the final regulatory decision on the naturally occurring asbestos, which was discovered this summer in one of Fairfax's prime development corridors. No other state or federal agency has claimed regulatory power.

"That's pretty much it until we hear something else," said Claude Cooper, county Department of Environmental Management director.

The discovery of the asbestos in a roughly 10-square-mile area had sparked a sensitive public relations problem for the prospering county. Initially, officials were reluctant to release information on the subject. The discovery prompted a series of meetings among county officials, consultants, and state and federal officials about the impact on development and worker safety.

Cooper said this week the county will continue to monitor the construction sites to ensure that the dust is controlled, which reduces the potential for asbestos to become airborne.

Officials have said that the airborne fiber content is too low to be covered by state or federal regulations designed to protect people from asbestos-caused cancers. Asbestos regulations tend to focus on schools and building materials.

Work at two construction sites, Fair Oaks Commerce Center and the Braddock Park high school, was temporarily halted in the summer when the asbestos was discovered. Some construction workers had complained of itching.

At the high school site, officials said tests show no asbestos health threat exists.

And at the Fair Oaks Commerce Center site near Fair Oaks Mall, the state's health enforcement director said inspectors recently placed portable pumps on construction workers to monitor the air they breathed during a normal work day. Test results show an airborne fiber count of less than 0.02 per cubic centimeters, lower than the 0.2 fibers per cubic centimeters considered permissible under worker safety laws, Wheeling said.

One month ago, representatives of the Heavy Construction Contractors Association, a trade group in Merrifield that represents ditch diggers, sat through a two-hour briefing by county officials on asbestos.

Robert B. Woodward, the group's executive director, said county officials seem to have the naturally occurring asbestos under control and added that he no longer has serious concerns. Woodward said colder weather, which has slowed the pace of construction, also has quieted concern.

"It sort of died a natural death," he said.