Robert H. O'Brien, 93, chief executive officer at Metro-Goldwyn-Mayer during a critical period in that studio's history. After the financial debacle of the remake of "Mutiny on the Bounty" in 1962, O'Brien became head of the studio and oversaw the production of some of MGM's biggest hits, including "Doctor Zhivago," "2001: A Space Odyssey" and "The Dirty Dozen." In 1965 O'Brien was named Pioneer of the Year by the Motion Picture Pioneers Assn. and in 1966 won humanitarian awards from both the March of Dimes and the Anti-Defamation League. Before entering the motion picture industry O'Brien had been with ABC and was a commissioner of the Securities and Exchange Commission. He left MGM in 1969 after a management dispute. In Seattle on Monday.