Increased earnings from its semiconductor products sector, which returned to profitability after operating at a loss in 1985, a substantial reduction in losses at Motorola Computer Systems and sharply higher operating profits in the the cellular group most contributed to Schaumburg, Ill.-based Motorola Inc.'s record sales and higher earnings for 1986. Sales and earnings also were higher in the fourth quarter. A spokesman said that in 1987, Motorola expects to be operating "in an environment of modest economic growth and intense global competition in electronics . . . the opportunity exists for continued sales growth and improved earnings performance."