FEW PEOPLE knew what a stun gun was before recent reports that the weapon had been used by police in New York City to elicit confessions from suspects in custody. The device is a hand-held, pronged instrument that delivers painful electric shocks and sometimes leaves burn marks. The New York scandal produced a storm of protest from both the city government and the public, and many police were transferred or forced to retire.

This week, a stun gun was used here in Washington for another purpose. The office of the U.S. marshal for the District of Columbia has confirmed that such a device was used to prod a man under arrest who refused to walk as an act of passive resistance. The prisoner was a 79-year-old clergyman who had taken part in a political demonstration organized by a religious group. The minister, Rev. Maurice McCrackin, says he received "a very heavy, stinging electrical charge to the legs seven or eight times."

Stun guns have been issued to police in many jurisdictions, and to U.S. marshals here, for a humane purpose. They are intended for defense, to be used as an alternative to deadly force in subduing an attacker. It was never expected that they would be used for torture or for prodding human beings as if they were animals. Rev. McCrackin's experience calls to mind the use of cattle prods by some southern sheriffs during the great civil rights demonstrations of the '60s and produces the same feelings of revulsion. This kind of assault is a sadistic response to passive resistance and is especially repugnant when the victim is elderly and frail.

Hubert M. Rutherford III, the U.S. marshal for the District of Columbia, has transferred the deputy involved in the McCrackin case and has initiated an investigation of the incident. He should also reiterate to the entire force the conditions under which stun guns may be used. Every officer must clearly understand that the devices are for defense only, and may never be employed to inflict pain or punishment on those in custody who pose no threat to others.