The Environmental Protection Agency last week released the government's first comprehensive nationwide survey of asbestos in commercial-type buildings, and said that about 20 percent of the structures contain building materials that could include cancer-causing asbestos.

In the past, asbestos was often used as an insulating material in walls and around pipes, and in ceiling and floor tiles.

The study focused on 231 buildings in 10 unspecified areas, including offices, warehouses, residential apartment buildings with more than 10 units and federal buildings. It was designed to be a statistically valid "baseline" to assess the dimensions of the nationwide health and safety threat posed by the substance, which can cause cancer when microscopic particles of it become lodged in the lungs.

"Residential rental units and federal government buildings had a higher incidence of asbestos-containing friable materials than private non-residential buildings," the report said. The study did not cover schools, which are being studied by other EPA divisions.

The study found that buildings constructed in the 1960s were more likely to have friable (easy to crumble) asbestos than were other buildings. "It appears that the extensive use of asbestos-containing sprayed-on friable materials would have continued and perhaps increased in the 1970s had not the EPA banned the use of those materials for all but decorative purposes in 1973," it said.

In 1978, the study noted, the EPA banned all other uses of asbestos in building construction; the agency is now considering whether to ban other, non-structural uses of asbestos, such as in brake linings.