A lieutenant commander on Tuesday became the fifth Navy official and the eighth person over all to plead guilty to federal charges in a bribery scandal involving ship-supply contracts in the Pacific. The lieutenant commander, Todd Dale Malaki, 44, admitted in federal court in San Diego that he had accepted more than $15,000 in cash, hotel stays and the services of a prostitute to help Leonard Glenn Francis, a Malaysian contractor, win Navy business. Mr. Francis and two of his former employees have also pleaded guilty to federal charges. Prosecutors estimate that they overbilled the Navy by at least $35 million for ship supplies and dock services.