The first trainload of heavy equipment donated by Los Angeles for use in Mexico City was given an enthusiastic send-off by city officials. The bulldozers, hydraulic jacks, torches and wrecking bars loaded on railroad cars were found to be the most needed by Mexicans who are searching for more earthquake victims and demolishing unsafe buildings. When air transportation could not be arranged, Union Pacific Railroad offered to ship the equipment free to Mexico via freight train, Mayor Tom Bradley said. The gesture was just one of many from Southern California since the Sept. 19 quake jolted central Mexico, killing more than 4,700 people. "We have been very fortunate that the people of this community have responded so well," Bradley said.