Two top managers of the Nuclear Regulatory Commission are retiring and the agency is reorganizing some of its top management posts.

The changes were announced Monday by NRC Chairman Shirley Ann Jackson, with the new organization taking effect Jan. 5.

James M. Taylor, executive director for operations, will retire in January, the agency said. He is to be succeeded by Leonard J. Callan, a regional administrator with the NRC.

The agency also announced the appointment of Samuel L. Collins, a deputy regional administrator, as director of the office of nuclear regulation. He succeeds William T. Russell, who retired in September.

Under the reorganization the executive director will be joined by a chief financial officer and a chief information officer, two new jobs both also reporting to the chairman of the agency. In the past the executive director has also handled finances. The new posts have not been filled.