In other rock benefit news, Bob Geldof, who helped raise more than $50 million with the 1985 Band Aid record and concerts, will return to Ethiopia this week to publicize the expected famine. The London Observer reported Sunday that the Irish pop singer would spend 10 days traveling to the most severely affected areas of the troubled African country. . . . And in San Francisco, Joan Baez and rock promoter Bill Graham have announced plans for a pre-Christmas benefit concert--featuring the Grateful Dead's Jerry Garcia and guitarist Bob Weir--to help destitute AIDS victims. The Dec. 17th concert will be broadcast live on San Francisco public television station KQED and may be televised on local stations elsewhere, Baez said.