Public safety officials at the Smithsonian Institution discovered fibers of asbestos, a potentially cancer-causing substance, in several basement-level rooms in the National Museum of American History last September, but won't begin to remove or cover the material until late spring.

In the meantime, the rooms remain open to the public. Robert B. Burke, director of the Smithsonian's Office of Protection Services, said he does not believe there are any dangers to the public, although a contractor is now being sought to remove some of the asbestos.

Asbestos insulation in ceilings in television, audio-visual and film studios will be covered or removed, Burke said. In addition, a dumbwaiter serving the studio area has asbestos tubing in it, and there is asbestos in a vestibule area near the three screening rooms.

Edward Sniechoski, chief of the Smithsonian's safety division, said tests last September by federal industrial hygienists showed that there were about 0.07 fibers per cubic centimeter. Sniechoski said that the critical level is 2.0 fibers per cubic centimeter, "according to a government standard."

But other government safety officials criticized the Smithsonian's standards as too lax.

"We would evacuate a federal building with a 2.0 fibers per cubic centimeter level; I've never heard of anyone using a standard that high," said Paul J. Chistolini, deputy assistant commissioner of building management at the General Services Adminstration. Chistolini's responsibilities include supervising asbestos-abatement procedures in most federally operated facilities, but not the Smithsonian.

Chistolini said that the Occupational Safety and Health Administration standard calls for no more than 0.1 fibers per cubic centimeter.

"Those Smithsonian standards are high. You won't find that, except near an asbestos manufacturing plant," said Paul Burnett, a GSA asbestos expert. "A high school in Massachusetts was shut down entirely because the readings were 0.06 fibers per cubic centimeter."

Studies show that asbestos fibers inhaled and lodged in the lungs may cause cancer.

"The asbestos was installed there when the buildings were built in the 1940s," Burke said. "We found it by looking; we have an aggressive program to find all kinds of dangers, including toxic chemicals, lead, noise pollution, radiation . . . . The most common thing we have found is pipes that were wrapped with asbestos. There are probably other things that have been missed (by inspectors) for 40 years. I'm convinced that there's some other asbestos somewhere that they're going to find."