AT&T; called for a probe of three spun-off firms.

The company asked the Justice Department to investigate whether three of the holding companies spun off when AT&T; was broken up have become involved in manufacturing telephone equipment, in violation of the breakup order. In a letter to the department’s antitrust division, AT&T; attorney Jim G. Kilpatric said acquisitions and joint ventures by BellSouth, Ameritech and Southwestern Bell may violate the consent decree that governs the activities of the former parts of the Bell System. The companies denied the charge.