Southern California Edison said Tuesday it was developing a plan that would lead to the eventual restart of the San Onofre nuclear power plant near San Diego. The Nuclear Regulatory Commission earlier in the day formally told Edison it would not allow the two reactors at San Onofre to restart until the company proved it had clearly understood the cause of \"unusual wear\" on steam generator tubes. \"Until we are satisfied that has been done, the plant will not be permitted to restart,\" Elmo Collins, NRC Region IV administrator, said in a letter to the utility. Edison, the majority owner of the plant, responded in a written statement it had recently completed an extensive inspection of the plant and would use the findings to develop a plan to correct any problems. \"We welcome the NRC\'s letter, which is a formal step in the process of restarting Units 2 and 3,\" said SCE President Ron Litzinger. \"The utility will only bring the units on line when we and the NRC are satisfied that it is safe to do so.\" The NRC letter was a response to a \"rapid shutdown\" of the Unit 3 reactor at San Onofre that occurred Jan. 31 after a tube sprung a leak. A subsequent inspection turned up signs of wear on several tubes that had been replaced in the past two years. The NRC said it appeared vibrations of unknown nature had caused several tubes to rub against one another or support structures within the generators. Unit 2 had been shut down earlier in the month for planned maintenance. Unit 1 was decommissioned in 1992. San Onofre has a total generating capacity of 2,200 megawatts, about enough electricity to power 1.4 million homes.