A LOT OF PEOPLE in Montgomery County are worrying over a highway-safety problem that became apparent last year: the possibility that road gravel may be a source of dangerous asbestos-laden dust. This is more than a local concern because serpentinite, the stone involved is found and used in road-building in many states.

Some things are known. The serpentinite, produced here by the Rockville Crushed Stone Company, contains about 1 per cent asbestos fibers. Asbestos causes mesothelioma, a rare form of cancer, which may appear 20 or even 40 years after exposure. Authorities do not yet agree, however, about how dangerous the gravel dust may be and what protective measures are required. The Environmental Defense Fund has emphasized the risk to children who use playgrounds covered with serpentinite or wait for shcool buses along gravel roads. EDF wants the federal Environmental Protection Agency to force the county to stop using the gravel and resurface 125 miles of unpaved roads , a job that could cost $7 million over five years.

Most county, state and EPA officials regard such steps as premature. Until analysis of air samples has been completed this summer, they say, they cannot even be sure how much asbestos dust is really in the air. Moreover, EPA has not decided how much, if any, of this kind of air pollution should be allowed. County officials and Rep. Newton Steers (R-Md.) have urged the federal agency to set a standard, but that process is bound to be controversial.

One might think that all this could be more rapidly resolved, especially in an area where so many talented scientists work and live. As in most environmental pollution cases, though, hard answers cannot be found - expect by waiting few decades to see how many victims appear. Thus policies have to be based on prudence and a careful assessment of risks and costs. Montgomery County has already stopped using the types of serpentinite gravel that generate the most dust. The next step, in our view, should be to resurface affected play areas and at least the more heavily used gravel roads. Other jurisdictions that have been using serpentinite should take such precautions, too, with help from the states, where needed. It may not be necessary or possible to stop using this stone altogether, but there's no reason o lea ve so many bits of it lying around.