Northrop Grumman Corp., Los Angeles, is merging three of its defined benefit plans with a total of about $12.3 billion in assets, to take advantage of the overfunded status of the Northrop Grumman pension plan. The plans are the Northrop Grumman pension, the companys largest plan with more than $11 billion in assets; the Electronic Sensors & Systems Division, with about $800 million; and the salaried portion of the pension plan of Vought Aircraft Co., with about $500 million, said Albert Myers, treasurer. State Street Bank & Trust is the master trustee for all the plans. "This change will not in and of itself cause any change in managers with whom the funds are invested, Mr. Myers said. The merger will eliminate $80 million a year in contributions that were being made to the Electronic Sensors plan, which was underfunded by a few hundred million dollars before the merger of the plans. The Vought plan was about "even-funded, and required no contributions before the merger of the plans, Mr. Myers said. The Northrop Grumman plan still will be overfunded in excess of $2.5 billion after the merger, he said.