Two electrical transformers in the White House complex were found to be leaking cancer-causing PCBs during a recent inspection by the Environmental Protection Agency, and the General Services Administration will start "retrofilling" the transformers with a nontoxic fluid next week, a White House spokesman said.

Spokesman Dale Petroskey said last night that neither of the leaking transformers serves areas of the White House where President and Mrs. Reagan live. He added that the EPA saw "no reason we should be unduly concerned" about the leaks, which were found in an electrical vault beneath West Executive Avenue, which runs between the White House and the Old Executive Office Building.

Petroskey said the leaking transformers were discovered during a July 30 EPA inspection and were sealed the next day. He said the inspection was requested by the White House after reports that transformers at the Smithsonian Institution were leaking PCBs. PCBs, or polychlorinated biphenyls, are used as a coolant in transformers because they are fire resistant. When they are involved in a fire, however, they produce dioxin, one of the deadliest chemicals. The manufacture of PCBs was banned in 1977.

Petroskey said the White House complex has 19 transformers, and three that serve the residential portions were retrofilled in December 1983, a process that replaces PCBs with a nontoxic coolant. He declined to say where those transformers are located.

Petroskey said the GSA next week will begin retrofilling the 16 remaining transformers -- all now cooled by PCBs -- and hopes to finish the project in about 30 days. No cost estimate was available on the project, he said, but a GSA spokesman said recently that it costs about $40,000 to retrofill one transformer.