When the police chief in Tacoma, Wash. shot and killed his wife in a parking lot after years of abusing her, the shock from that event 10 years ago mobilized national support for a more aggressive response to domestic violence in police households. While police officers today are more aware of the problem, the following is also true: In many departments, an officer will automatically be fired for a positive marijuana test, but can stay on the job after abusing or battering a spouse. In the wake of the Tacoma killing, the International Association of Chiefs of Police strengthened its efforts to persuade departments to adopt a set of model rules on domestic violence in their own ranks. Responding to concerns that domestic violence had long been treated more leniently than other forms of misconduct, the organization called for zero tolerance for abusers, tougher pre-employment screening and a separate set of procedures to ensure rigorous investigation of every accusation. But police departments have been slow to adopt the rules. And while most officials say they treat domestic abuse by officers as they would any other form of misconduct, interviews and disciplinary records indicate that, in fact, punishment is often light and job loss uncommon. Only a quarter of the 56 largest city and county police departments that responded to a recent survey have a distinct policy for domestic violence involving officers. And only one, Nashville, has adopted the entire model policy, according to the survey, conducted by The New York Times and the PBS investigative news program “Frontline.” Three others — Charlotte, N.C.; Chicago; and Columbus, Ohio — follow most of its provisions.