The Southern Railway System gave its two top executives promotions yesterday.

L. Stanley Crane, 64, president of the Washington-based railroad since February 1977, moved up to chairman and chief executive officer, a new position on the organization chart.

Harold H. Hall, 53, executive vice president for operations since 1977, might be allowing Hall to assume.

Southern announced the changes late in the day, but offered no explanation of how the new titles will change the duties of the railroad's two top men.

Crane is nearing retirement age, and there was speculation that he might be allowing Hall to assume broader responsibility for Southern's management.

Crane served as executive vice president for operations until he was named president and chief administrative officer. He had been expected to assume the chairman's job since W. Graham Claytor Jr. left that post to become secretary of the Navy in 1977.

Crane was named the railroad industry's "chief executive of the year" in 1978 by Financial World magazine. He has worked for Southern since he graduated from George Washington University in 1938 except for 18 months as an executive of the Pennsylvania Railroad in the early 1960s.

Hall, who became vice president for operations after Crane was promoted joined the railroad as a depot agent and telegrapher in 1943 and moved up through the ranks. He was elected to the board of directors last year.