A survey by a major labor union that represents 100,000 school employes reports that people in 10 percent of the nation's schools may be exposed to potential cancer risks from crumbling forms of asbestos.

The figures were released at a press briefing yesterday by the 750,000-member Service Employees International Union, the White Lung Association, and a cancer researcher. The survey said that 20 states across the country have violated a U.S. Education Department rule requiring records on school inspections and that 3.2 million children and 648,000 school employes across the nation have "potentially" been exposed to asbestos.

Public school officials in the District, Northern Virginia and Maryland said that although asbestos had been a problem in some schools, they no longer considered it to be a major concern.

The sponsors of the press briefing, including union president John J. Sweeney, said that the figures cited were a projection based on data from 11 states "which have apparently accurate record-keeping systems." Others at the briefing acknowledged they did not have detailed data on the extent of the problem of asbestos in schools.

"We have no idea what the dimensions of the problem are," said Dr. Marion Moses, a researcher who works with the Mt. Sinai School of Medicine, "but we shouldn't wait until we know."

Studies have linked the inhalation of airborne asbestos fibers to lung and other cancers since the 1930s, but evidence did not begin to mount until the 1960s. In 1973, the Environmental Protection Agency banned the use of spray-applied asbestos insulation in school buildings.

More recently, the EPA set a June 28 deadline for inspection for the presence of "friable" (flaking, crumbling, powdery) asbestos in schools. But an EPA official said that the rule does not extend to telling schools what procedures should be employed in the event that friable asbestos is found.

Officials in Maryland, Virginia, the District, and EPA spokesmen in general, say most of the asbestos problems have been solved.

"Most places in Virginia do not have serious problems. I haven't heard of any problems in Northern Virginia," said Martha S. Phillips, assistant supervisor of the energy and facilities service of the Virginia Education Department.

The union survey said that 43 Virginia school districts have found friable asbestos and only 20 have taken action to remove or "encapsulate" it.

Officials in Montgomery County and the District say that 15 schools in those juridictions had asbestos problems that were solved between seven and three years ago.

A Prince George's school system spokesman said that within the last few months work has been required to bring 23 of the county's 174 schools into compliance with new and more restrictive standards. He said work on the last of the 23, Northwestern High School, will be finished by July 13, but will require shifting about 500 summer students to the Hyattsville Middle School.