VERSAR <VSR> TO BUY MARIETTA <ML> UNIT Versar Inc said it has agreed in principle to acquire Martin Marietta Corp's Martin Marietta Environmental Systems unit for about 5,300,000 dlrs. Versar said it would use its working capital and an established life of credit to find the purchase, which is subject to approval by both boards and is expected to be completed in April. Marietta Environmental had 1986 revenues of about nine mln dlrs. Versar said the acquisition should have a "moderately" favorable effect on its earnings this year.