MARYLAND'S STATE POLICE are swift and efficient in their pursuit of speeding motorists but not in recruiting or promiting black and female troopers. Notwithstanding the threat of a U.S. Department of Justice suit, the signing of a consent decree five years ago and an extension of the decree in May of this year, the force is still about 93 percent white and 98 percent male. Until this month, all but two of the department's 108 black troopers held ranks below corporal. After a group of black troopers complained, three blacks were promoted to corporal, and they and a black sergeant were given supervisory jobs.

Now, at least, federal and state authorities seem agreed on a reasonable plan to improve minority hiring and promotions. The original concent decree called for 16 percent of the force to be black by 1979. But this goal did not fairly take into account the general cutbacks in hiring that ensued after the goal was set. The new modified decree makes more sense: to make 14 percent of new hires minority people, and to step up minority recruiting.

Important, too, is the response of State Police Superintendent Thomas S. Smith. Besides recruiting and promoting black and female troopers, Col. Smith is starting sensitivity training sessions for all members of the force. These moves should make the state's chief law-enforcement agency more responsive to and reflective of the public it is meant to serve.