By: Editorial Staff AFTER A MEETING with representatives from the National Newspaper Association, the U.S. Postal Service has withdrawn a rule that would have burdened community newspapers with long and costly computations on forms for second-class mailings. NNA chairman Frank W. Garred, publisher of the Port Townsend (Wash.) Jefferson County Leader, and NNA Government Relations Committee chairman Jack Fishman, president of Lakeway Publishers Inc., Morristown, Tenn., in December made a personal plea to Postmaster General Marvin Runyon regarding the rule. Also at the meeting was NNA president Tonda F. Rush. According to the NNA, Garred and Fishman told Runyon the rule would force small newspapers to purchase sophisticated weighing equipment and to carry out time-consuming computations. The rule, slated to go into effect last March, was postponed for a year and would have become effective March 15, 1993. Instead, it has been withdrawn completely.