The reorganization of American Telephone & Telegraph Co., the largest corporate restructuring ever, moved closer to reality yesterday as the Justice Department approved the phone company's plans for divestiture of its wholly owned operating companies next Jan. 1.

In papers filed in U.S. District Court, the department recommended a dozen modifications in the AT&T proposal, primarily of a technical nature. For example, Justice urged that all public phones be owned by the operating companies.

AT&T announced that it was willing to accept the modifications and asked the court to approve the plan.

One of the most significant changes involved Charge-A-Call telephones, which accept special credit cards, but not coins, for long-distance calls. AT&T had argued the Charge-A-Call phones were used almost exclusively for long-distance calls and thus should be assigned to it.

The Justice Department disagreed, however, stating: "Charge-A-Call phones have been installed by the Bell companies as part of the service the local telephone company provides to the public."

The Justice Department also decided the Bell companies should be allowed to directly sub-license certain equipment patents after the breakup instead of going through AT&T, and that the Bell companies should control the assignment of "800" telephone numbers needed for in-bound WATS service.

The plan calls for AT&T to spin off its 22 operating companies into seven regional operating groups. The Mid-Atlantic regional operating group--which will be based in Arlington--will consist of Diamond Bell of Delaware, New Jersey Bell, Bell of Pennsylvania and the four Chesapeake & Potomac companies.

The Justice Department did reserve the right to make additional suggestions after the states and other interested parties file their comments by April 13.

U.S. District Judge Harold H. Greene is expected to rule shortly whether the proposed plan, with amendments, conforms to the settlement agreement between Justice and AT&T.