About 400 employes at the U.S. Department of Health and Human Services were sent home Wednesday afternoon after safety specialists discovered that workers in the agency's North Building were being exposed to potentially dangerous asbestos, government officials said yesterday.

Subsequent tests showed the amount of asbestos fibers in the air did not exceed federal safety standards, according to the General Services Administration, which is responsible for government buildings, and all but 10 employes returned to work yesterday.

Those 10 workers -- employed in the print shop in the building's basement where the asbestos was found -- were told to return to work today after additional tests showed their level of asbestos exposure also was "nondangerous," GSA officials said.

But Wednesday's "asbestos scare," as one employe called it, has revived concerns that current maintenance and asbestos cleanup practices at the HHS building, at Independence Avenue and Fourth Street SW, are exposing workers there to potentially health-threatening airborne asbestos.

Exposure to asbestos -- a substance once widely used for insulation, acoustical and fireproofing purposes until it was banned in 1972 -- can scar the inside of the lung, causing asbestosis and other diseases, including a rare form of cancer, according to researchers.

"Anything in the air can cause a problem," said Joe Cook, president of the American Federation of Government Employees, Local 41, which represents several groups of workers at the agency. "Anytime asbestos gets airborne, it can spread and get into the ventilation system."

Cook disputed GSA and HHS claims that the asbestos levels, measured in the number of fibers per cubic centimeter, were so low as to be nonthreatening. He said federal standards concerning asbestos exposure are based on 20-year-old measurements taken in industrial settings where there is better air circulation.

Office employes, working in confined quarters, are more at risk from asbestos exposure, said Cook. He said both the Environmental Protection Agency and the National Institute for Occupational Safety and Health have advised workers that there is potential danger from exposure to any fibers.

The potential asbestos hazard occurred about 12:30 p.m. Wednesday during replacement of a pipe in a cooling system at the building's northeast corner.

A government safety inspector, finding dust and other residue on the basement floor, alerted HHS and GSA officials.

As a precaution, workers on five floors at the northwest corner of the building were sent home on administrative leave with pay at 3 p.m., pending test results.

The tests showed airborne asbestos levels were between .006 and .01 fibers per cubic centimeter, according to Dale Bruce, spokesman for GSA's regional office here. He said the agency would not become concerned unless exposure levels reached .03.

But Cook said yesterday that an on-site inspection, performed by an outside consultant for the agency's special asbestos abatement task force, showed the asbestos was being improperly removed at the time of exposure and that procedures designed to avoid stirring up dust and contaminating workers were being ignored.

According to the report, Cook said, "there was active open drawing [into the building's ventiliation system] of potentially contaminated air."

Bruce said GSA had contracted with the John C. Grinberg Construction Co. to repair the cooling system, which in turn had subcontracted with Southern Insulation, Inc. to remove the asbestos from around the pipes. He said the agency has asked its own safety consultants to monitor further repair work to make sure proper asbestos removal procedures are being followed.

Richard Swim, a representative on the asbestos abatement task force for the Federal Managers Association, said GSA and HHS acted swiftly to insure worker safety. He said the asbestos hazard in the building is well-known and must be constantly monitored.