The Justice Department and American Telephone & Telegraph Co. apparently moved a step closer to settling the government's antitrust suit against AT&T yesterday as both sides told a federal judge that settlement negotiations are proceeding on track.

But the Justice Department said in a letter that the Reagan administration's new chief of the Antitrust Division would be charged with evaluating the proposed settlement package. The letter was signed by Charles Renfrew, the Carter administration's deputy attorney general, who will hold his job until his successor is confirmed. Attorney General William French Smith has decided not to participate in the case because he was a board member of an AT&T subsidiary.

No successor has been named to Sanford Litvack, the assistant attorney general for the Antitrust Division, although Wesley Leibeler, a law professor at the University of California at Los Angeles and a frequent critic of federal antitrust policies, is apparently the leading candidate.

The decision to assign the case to Litvack's sucessor and not Edward Schmults, a New York lawyer whose nomination as deputy attorney general is awaiting confirmation, means there is no guarantee that Litvack's replacement will be in office by March 4 deadline imposed by U.S. District Judge Harold Greene for presentation of a settlement.