The Justice Department today backed Ameritech Corp.'s drive to provide long-distance telephone service for Chicago, Ill. and Grand Rapids, Mich. Ameritech would be the first baby bell to get into the $68 billion long-distance business since the 1984 breakup of AT&T. It is seeking permission from federal Judge Harold Greene, who oversees the decree that splintered AT&T. Ameritech officials explained that they want to re-sell long-distance service provided by other companies. In turn, the firm would agree to make it easier for others to provide competing local phone service. This is the first time both AT&T and the government are backing such a request.