Thousands of New York City firemen marched across the Brooklyn Bridge and surrounded City Hall, tying up traffic to protest city tactics used in the closing of a firehouse. The demonstration underscored outrage over the methods used to shut Engine Company 232, in Brooklyn's Brownsville section, as part of an effort to trim the city budget. Last month, the Fire Department's top chiefs ordered firefighters from the station to travel without further instructions to another firehouse--a common emergency measure. But when the firefighters arrived, they were told that their own quarters were being closed. They were then taken back to the firehouse and escorted in to pick up personal belongings.