Martin Marietta Corp. reported 1987 earnings of $230.6 million, compared to $202.3 million in the prior year. Sales reached a record high of $5.165 billion from $4.752 billion a year ago. Firm backlog of undelivered orders at year-end was $10.8 billion, also a new high. Fourth-quarter net increased to $59.4 million from $43.4 million. Sales rose to $1.34 billion from $1.268 billion. The Bethesda, Md., firm said it realized sales and earnings gains in all four of its business groups: electronics and missiles, astronautics, information systems and materials.