South Korean baby girls joined at the hip will undergo an operation in Singapore Tuesday to be separated. The medical staff at Raffles Hospital plan to begin the operation around noon if the physical condition of the four-month-old twins is deemed stable. The doctors said they are optimistic about the operation, since the joined part of the girls is not too difficult to separate, and have put the chances for success at more than 85 percent. Joined at the tail bone at a slight angle, the twins can lie down only on one side.