Security Pacific Corp., Los Angeles, said its Security Pacific Automation Co. unit has agreed to acquire Summit Information Systems Corp., Corvallis, Ore., for an undisclosed price . . . Atari Corp., Sunnyvale, said it has purchased the creditor position of about $32 million in the Federated Group Inc., its wholly owned consumer electronics retailing chain, from five banks led by Security Pacific National Bank . . . Santa Cruz, Calif.--based Plantronics Inc. said it would not pay its regular quarterly dividend of 4 cents a share for the fourth quarter of fiscal 1988.