he Environmental Protection Agency, alleging that Commonwealth Edison Co. accidently discharged PCBs in three places and did not tell people who were contaminated, filed suit seeking $280,000, the largest penalty it has ever requested.

The EPA also filed suit against North Shore Gas Co., a Waukegan-based concern, seeking $29,000.

The Commonwealth Edison suit stems from three alleged spills of polychlorinated biphenyls, a suspected carcinogen, in the west Chicago suburb of Oak Park and the southwestern suburbs of Tinley Park and Lansing, said Valdas Adamkus, EPA regional administrator.

The EPA charged that pole-mounted capacitors, which store electrical charges, ruptured at each location, discharging fluid that contained PCBs and contaminating people and property. The agency also alleged that Commonwealth Edison did not tell those people contaminated by the discharge that the fluid contained PCBs.

Further, the complaint charged, Commonwealth Edison's "cursory" cleanup did not "fully or properly" remove high levels of PCB contamination.

The EPA's complaint against North Shore charged it with burying "several" 55-gallon drums of oil containing PCBs on its premises in 1980, then denying it to EPA investigators. Acting on a tip, the investigators dug up the drums. Tests confirmed the presence of PCBs, the suit claimed.

Neither utility would comment last night.