A Massachusetts firm, working under a federal research grant, has developed a portable device that could help detect airborne asbestos hazards in schools and thousands of other buildings constructed with the cancer-causing mineral. Federal environmental officials said yesterday that the device, known as a fibrous aerosol monitor, is being tested in some schools and has been used in several shipyards where airborne asbestos released during construction has posed a health hazard.

The monitor was built by the GCA Corp. of Bedford, Mass., with funding from the Bureau of Mines, the National Institute for Occupational Safety and Health, and the Environmental Protection Agency.

The device is the size of an attache case, and costs about $9,000, according to the manufacturer. It measures laser beam fragments scattered by spinning particles in an air sample in a small tube. The monitor is able to pick out which pulse of light comes from fibers as small as one ten-thousandth of a centimeter.

A spokesman for the Massachusetts firm said, however, that the monitor cannot distinguish between asbestos and other minute fibrous particles in air. "Once you know you have asbestos, you can measure how much is getting into the air," the spokesman said.

Concern about asbestos in schools and other public buildings has becone widespread since last year, when then-secretary Joseph A. Califano Jr. of Health, Education and Welfare issued a warning to all 50 governors that asbestos had been found in New Jersey schools. "Any exposure probably carries some risk of disease," Califano noted.

Since then, EPA investigators have estimated that as many as 10,000 of the nation's 90,000 schools could contain asbestos materials.

But federal experts have said that the real problem is not the presence of asbestos in building material. They said the problem is detecting airborne asbestos or situations where the mineral can be shaken loose into the air. Cancer experts say that breathing even minute amounts of asbestos can cause cancers 20 or 30 years later.

Testing for airborne asbestos is usually done by collecting air samples drawn through a material and counting the number of fibers of asbestos that appear on a sample under a microscope. The process is costly and uneven, and takes weeks to complete, criticis have complained.

Several federal experts yesterday expressed cautious optimism that the new portable monitor could speed up detection of asbestos in schools under certain conditions.

Paul Baron, a NIOSH physical scientist who headed that agency's assessment of the monitor, said he tested it in several Kentucky schools where asbestos was being shaken loose during construction.

"It seemed to work well," he said. Baron noted that the device could not pick out asbestos fibers separately, but, he said, "it will tell if there are no fibers present and it will give an immediate result instead of waiting for weeks, which could be too late."

An EPA spokesman said the agency was testing several monitors. Joseph Breen, an EPA researcher, said the device can pick up asbestos "hot spots," but that it cannot detect extremely low levels of the mineral that EPA is investigating in schools.