Naturally occurring asbestos has been identified in rock samples taken from more than two dozen locations in Fairfax County, according to a county report released yesterday, suggesting that the asbestos problem is more widespread than officials previously indicated.

The rock samples came from sites including Lake Fairfax and Oak Marr parks, construction areas, telephone cable trenches, power line easements and a real estate office, according to the inch-thick report. The asbestos content in the samples ranged from 1 to 100 percent, the report said.

In some forms, asbestos has been shown to cause cancer. Officials say the substance becomes a potential health threat when it is disturbed and dispersed into the air.

County officials have said that there appears to be no health threat because the rock samples' airborne fiber count, as opposed to their asbestos content, is very low. State officials have said the airborne fiber count appears to be too low to be covered by state or federal regulations designed to protect people from asbestos-caused cancers, but cautioned that more specific testing was needed. Local officials are seeking state and federal guidance.

Deputy County Executive Denton Kent said yesterday that the county health department will monitor construction sites to ensure that precautions, such as controlling dust, are taken to reduce the potential for asbestos fibers to become airborne.

Before yesterday, county officials had said that airborne asbestos fibers had been found at two construction sites, the Fair Oaks Commerce Center and Braddock Park High School, both in west-central Fairfax. Work at those sites was temporarily halted.

The bulk of the asbestos-bearing rock is in a roughly 10-square-mile area that is part of a prime development corridor curving to the west of Fairfax City, including the Little Rocky Run subdivision, according to the report.

In addition, patches of land in northern Fairfax and near Great Falls Park were identified in the report as having asbestos-laden rock.

Until now, county officials had been reluctant to release information concerning their discovery this summer that almost 7,000 acres near Fair Oaks Mall could be embedded with pockets of asbestos.

At a County Board of Supervisors meeting Monday, Vice Chairman Martha V. Pennino (D-Centreville) questioned County Executive J. Hamilton Lambert about the problem. Lambert responded that news reports had blown the issue out of proportion and said additional information would be made public this week. Lambert was in Dallas yesterday and unavailable for comment.

Yesterday's report indicated that county officials have had a flurry of conversations with consultants and other officials about the asbestos problem. Regulations on asbestos have been aimed at schools and building materials; naturally occurring asbestos seems to have fallen into the regulatory cracks.

Next Thursday, officials from the state's Department of Mines, Minerals and Energy plan to tour some of the Fairfax construction sites, although they said yesterday that their role is still unclear.

Members of the development community, meanwhile, said they have many unanswered questions.

"We're waiting on what they are going to do," said Robert B. Woodward, executive director of the Heavy Construction Contractors Association, a 150-member trade group in Merrifield that represents ditch diggers. "If they don't know what to do, the ones who are going to end up getting it in the neck are our guys," Woodward said.

Of the six minerals called asbestos, two have been found in the rock samples from Fairfax -- actinolite and tremolite. The samples have contained mostly actinolite, which is not usually fibrous, but in this case has been found growing as fibers within pockets of deformed rock.

When the mineral grows as very long fibers, it is defined as asbestos, according to Malcolm Ross, a research mineralogist for the U.S. Geological Survey, part of the Interior Department.

County officials have said the asbestos-bearing band of rock found in Fairfax is common throughout Virginia and the eastern United States. But some experts on the subject have rejected that view, saying that every rock formation has its own geological history.

Meanwhile, county officials said they may bury the mounds of asbestos-bearing rock under 1 1/2 or 2 feet of soil, or use it as fill.

In the interim, Woodward, executive director of the Heavy Construction Contractors Association, said he is "just sort of sitting and watching this Ping-Pong ball go back and forth, wondering where it's going to land."