EAST CHICAGO — ArcelorMittal officials have announced plans to layoff nearly 1,000 workers at the steelmaker’s Indiana Harbor plant. Company officials announced a “mass layoff” at the Flat Carbon facility, where the steelmaker recently idled the No. 4 blast furnace, a letter to local union leaders states. Workers will be laid off “for an indefinite period of time during the 14-day period commencing on July 12, 2009,” a letter to United Steelworkers Local 1011 from General Manager Mark Whalen states. The sagging economy, particularly the deep slump in auto manufacturing, has caused steep declines in demand for steel — less...