(By The Associated Press) DALLAS, April 28--The longest dirt track automobile race ever held in the southwest is planned to be run at Fair Park, Dallas, Sunday, May 13.. The race will be 250 miles and will be one of the ten major automobile events held in this country during 1928. A field of 30 drivers is expected to start the race. Entry blanks have been mailed out to more than 50 of the best dirt track drivers in America. The track will be reconditioned. The turns will be banked and the Straight-a-ways put into a good shape. city had no jurisdiction.