THE LATEST reform to be announced in the Soviet Union promises to end use of psychiatry as a weapon against political dissidents, religious believers and others. This has been one of the most horrible Kremlin practices, applied against hundreds if not thousands of citizens. Torture and maltreatment by police are indefensible. Torture and maltreatment by doctors doing the work of police are the mark of savagery -- not the unreal ''doctors' plot'' of Stalin's fantasy but a real one.

The changes said to be forthcoming would touch not only the relatively few who are dissidents, but the many who are mental patients as well. Evidently family members will now be able to appeal a relative's involuntary commitment. No society, not even a democratically ordered one, operates easily at the intersection of law and medicine. How Soviet society, given the way it is ruled, will operate there is anybody's guess.

But the matter of forcibly hospitalized dissidents remains special. If the official statements on the new dispensation are true, then any of the dissidents still incarcerated should be released, and no new cases opened. The burden will be on the authorities to permit enough independent investigating and reporting to convince other Soviet citizens that these atrocities are at an end.

Here one must ask how much credibility the Kremlin can expect while leadership of its medical establishment remains in the hands of men identified as practitioners or apologists of political abuse of psychiatry. The man who would administer the reforms is Minister of Health Yevgeny Chazov, whose status as a Nobel peace laureate and Kremlin physician does not undo years of service defending vicious official policies. The acting head of the All-Union Center for Mental Health, Dr. Marat Vartanyan, is known for similar service. The president of the Soviet Society of Psychiatry, Dr. Georgy Morozov, himself certified the ''reformist illusions'' of dissidents by way of dispatching them -- isolated, drugged and often bound -- to years of terror.

In some of his reforms, Mikhail Gorbachev is putting new people in charge, realizing how deadly it is to keep on the people who were responsible for and comfortable with the old policies. In psychiatry, he appears to be leaving in place some of the old people. When men like Drs. Chazov, Vartanyan and Morozov are identified in Soviet print and removed from their positions, others will know the Soviet Union is serious about rooting out the sickening practices associated with their names.