D.C. Assistant Police Chief Ronal D. Cox, whose command includes the city's highly visible narcotics operation, has accepted a $67,000-a-year job as a public safety official with the Tennessee Valley Authority, TVA officials confirmed yesterday.

Cox, 45, a 24-year veteran, will retire from the D.C. force next month and start in mid-October in a position in which he will be responsible for assuring safety at the federal agency's 45 power-generating plants, including four nuclear plants. The TVA's facilities generate revenue of $4 billion a year and serve 3 million customers in an 80,000-square-mile area.

Cox declined to comment on his new job yesterday but acknowledged that he had withdrawn his name as a candidate for Maryland State Police superintendent. His decision came as Maryland officials were set to announce his appointment to that $59,800-a-year post, and the search for a new superintendent was resumed.

Maryland officials will consider four other candidates recommended by a search committee last month and will again contact other applicants who were not available for the post when they were first interviewed, said Bob Douglas, a spokesman for Gov. William Donald Schaefer.

Cox told Bishop Robinson, Maryland's secretary of public safety and correctional services, that the TVA post was "an offer he couldn't refuse," citing better salary and benefits and Tennessee's proximity to his family in Alabama, Douglas said.

The Maryland State Police has been without a superintendent since Col. George Brosan resigned in late April at Robinson's request.

TVA spokesman Craven Crowell said Cox "will be a key player in an ongoing management review and in the restructuring of the 1,000-member public safety service. We're delighted to get him down here."