Maryland officials say Montgomery County's longest-serving chief executive is expressing interest in becoming the general manager of the Washington-area rail system. The two officials spoke on condition of anonymity because former County Executive Douglas M. Duncan has not publicly discussed his interest in the Metro job. They say Duncan called them this week to say he wants to be considered. Both officials are monitoring the selection process. Duncan did not immediately return a call seeking comment Friday. Metro General Manager John Catoe announced last month that he is stepping down. His last day will be April 2. Catoe's announcement was made after a series of accidents, including the most deadly in Metro's history. The June 22 Red Line crash killed nine people.