Hilles Library will be closed for the next two days while technicians remove material believed to cause cancer, Facilities Maintenance officials said yesterday.

Workers from Westinghouse and Transformer Systems, Inc. will flush polychlorinated byphenyls (PCB's) from the library's central transformers, which lower the voltage of electrical current that enters the building, said John E. Cady, the assistant manager of Facilities Maintenance.

The toxic fluid will be transported to the Disposal Treatment Center in Boston, Cady said.

PCB's from a highly toxic chemical compound that insulates many large capacitators and transformers used by electric utilities.

Although PCB's are known to be highly toxic, they have not been proven to cause cancer, said Enviromental Protection Agency scientist Anthony Palermo.

Officials at Harvard's Facilities Maintenance office said the PCB's have not been a health hazard to library users.

The PCB's will be removed so that they would not leak in the event of an accident, said Facilities Maintenance Projects Manager Warren F. Clancy.

PCB's in transformers are not dangerous but assume a highly toxic gaseous form when exposed to the air, Palermo said.

Once released into the environment, PCB's pose a health risk for years, Palermo said.

If an accident caused a chemical leak, "we could be shut down for months and have serious health risks," Cady said.

A federal law requires that all transformers containing a PCB concentration of 500 or more parts per million be removed from commercial locations by 1990, Clancy said. He refused to disclose the PCB concentration on the Hilles transformers.