The Singer Co. on Thursday said it will sell its Electronic Systems and HRB divisions for a total of $455 million as part of Florida investor Paul Bilzerian's plan to finance his buyout of Singer. Plessey North America Corp. will acquire Singer's Electronic Systems Division for $310 million and the Hadson Corp. will acquire the company's HRB Division for $145 million, Singer said in a statement. The Electronic Systems Division, headquarterd in Wayne, N.J., produces airborne computers, radar navigation systems, tactical electronic equipment and other advanced electronic systems for the defense industry. It employs about 3,400 people and had revenues of $166 million in 1987. Plessey, a wholly owned subsidiary of the Plessey Co. of London, also produces electronic systems for defense and commercial use. ``The involvement of Singer Electronic Systems in advanced technologies used by the free world's defense forces adds important new business capabilities to Plessey,'' said Plessey Chairman and Chief Executive John Clark and Bilzerian, Singer's chairman and chief executive, in a joint statement. ``Singer Electronic Systems, in turn, will benefit in the worldwide defense electronics industry and is committed to growth in that field,'' they said. Singer and Plessey expect completion of the deal within 60 days. The HRB Division, based in State College, Pa., develops signal interception, processing and analysis systems, principally for U.S. government intelligence operations. It employs about 1,700 people and had revenues of $119 million in 1987. Hadson, based in Oklahoma City, Okla., is involved in defense, intelligence and space systems through its subsidiary, Ultrasystems Defense and Space Inc. The company is projecting revenues of $800 million in 1988, compared to $16.7 million in 1984. Singer and Hadson expect to complete the sale by the end of August. Singer will receive $137 million in cash and 2 million shares of Hadson common stock, representing 5.4 percent of Hadson's total common shares outstanding. ``We elected to take part of HRB's purchase price in Hadson shares because of the exceptional fit between the company's defense operations and HRB,'' Bilzerian said. ``We are convinced that this acquisition and the company's other plans for growth give Hadson a brilliant future. Therefore, our investment in Hadson's common stock is totally supportive of its current management,'' he added. The divisions are the fourth and fifth to be sold since Singer was acquired earlier this year by a partnership headed by Bilzerian. In making the acquisition, Bilzerian said at least part of the company's operations would be divested.