Martin Marietta Corp., a diversified manufacturer with operations in aluminum, cement, aerospace and construction materials, reported record earnings and sales for the second quarter of 1977. J. Donald Rauth, the firm's president, predicted this year would be Marietta's best ever.

Net earnings for the second quarter increased to $31.1 million 1.31 per share) on sales of $370.7 million, as compared with earnings of $23.1 million (98 cents) on sales of $316.5 million in the corresponding 1976 period.

United Nuclear Corp. reported earnings for the first quarter ended June 30 of $6.5 million ($1.02), a 44 per over last year's first quarter. Revenues for the quarter increased 66 per cent to $57.1 million as compared with $34.3 million in the prior year.

Union Trust Bancorp, holding company for the Union Trust Company of Maryland, reported earnings of $1.9 million (77 cents for the second quarter. For the six months ended June 30, earnings were $3.8 million ($1.53), compared with $3.7 million ($1.52) on the same date in 1976.

General Kinetics Inc. of Rockville, Md., reported net income of $590,000 (80 cents) on sales of $3 million for the year ended May 31. This compares with a net income of $100,000 (14 cents) on sales of $2.7 million for the previous year.

Doughtie's Foods Inc. of Portsmouth, Va. reported second quarter earnings of $174,000 (28 cents) on sales of $6.5 million, compared with earnings for the same period in 1976 of $125,000 (20 cents) on sales of $6.1 million.

For the six-month period ending June 25, earnings for the food processing and distribution firm totaled $269,000 (43 cents) on sales of $13.2 million, compared to $200,000 (32 cents) on sales of $11.4 million in 1976.