This episode's headline: Ethiopian Famine; Setting Limits; Education of a Teacher; Christmas in Washington. The guests include In Washington: ANNE SOMERS, Robert Wood Johnson Medical School; In New York: Dr. DANIEL CALLAHAN, Medical Ethicist; Dr. ROBERT BUTLER, Mt. Sinai Medical School; REPORTS FROM NEWSHOUR CORRESPONDENTS: DON MURRAY, CBC; ROGER ROSENBLATT; JOHN MERROW; ROGER MUDD. Byline: In New York: In Washington: JIM LEHRER, Associate Editor