NEW YORK, Oct. 2) (Kvon? Two medium-sized U. S. merchant ships were sunk in an attack on a Russian-bound convoy last July i} was learned today following fofticual announcement by othe r navy department. At least five crew members and possibly more were lost, the navy I said. Survivors, including Capt. George F. Sullivan and Capt. Jnesha Jacobson, masters of porn vessels, have been land «ad at a east coast port. They described the sinkings the re sult of a combined air and heat attack. Officers and members of the crew a were high in their praise of navy gunners aboard the ships who brought down two of the at tacking planes and remained at their posts until the ships settled, firing at planes and submarines.