Victor Stello Jr., 64, a former civilian nuclear power regulator who played a key role in the response to the accident on Three Mile Island, died Jan. 22 at his home in Potomac. He had cancer. Until recently, he had served as a principal deputy assistant secretary at the Department of Energy, focusing on safety and quality in defense programs. He came to the department in 1989 and worked in many areas highlighting his expertise in nuclear operations safety. "He instilled a serious safety culture in everything we do," said Dr. Victor Ries, the department's assistant secretary for defense programs. Mr. Stello also spent nearly a quarter of a century with the Nuclear Regulatory Commission and its predecessor, the Atomic Energy Commission. He was involved in the response to the country's worst commercial nuclear accident at the Three Mile Island nuclear plant near Harrisburg, Pa., in 1979. Stello later served as the NRC's chief of staff. In 1989, Mr. Stello was nominated by President Bush to head the Energy Department's nuclear weapons production program. He withdrew his name following a lengthy fight in the Senate to block his confirmation after nuclear critics accused him of improprieties during his tenure with the NRC. The Defense Nuclear Facility Safety Board recently gave Mr. Stello an award for his work as a proponent of nuclear safety. The safety board will administer the award--which is named for Mr. Stello--annually.