Gov. George Deukmejian has appointed Assemblywoman Sally Tanner (D-El Monte) to his task force on waste, energy and technology, which has been asked to formulate a waste management plan for the state by May 1, 1986. Tanner, who heads the Assembly Committee on Environmental Safety and Toxic Materials, said she welcomes the appointment but still believes the governor erred earlier this year when he vetoed her hazardous waste management legislation, which was a product of a similar task force effort. "I still find it hard to understand why the governor vetoed a bill which members of his own Administration were instrumental in developing," Tanner said. "Since those same administrators will be on the task force, I am hopeful that we can work together to develop positive solutions."