Dissident psychiatrist's acidic views; The Therapeutic State, by Thomas Szasz. Buffalo, N.Y.: Prometheus Books. 360 pp.

Thomas Szasz is an outspoken iconoclast, a dissident psychiatrist waging his personal unrelenting crusade against what he perceives as the psychiatric priesthood.

The author of 17 other books, the most famous of which is probably ''The Myth of Mental Illness,'' Dr. Szasz obviously derives great satisfaction in attacking and unmasking what he considers to be the pretentious quackery of his chosen profession.

''The Therapeutic State'' is a collection of short essays, all but two of which have been previously published in various magazines and professional journals.

The essays are grouped into seven themes: ''mental illness'' (the psychiatrist's bogeyman); mental-health policy (the ''Church of America''); the insanity defense (which he would term ''inane'' if he believed in that concept); psychiatry and politics (in which he decries the use of psychiatric cant as a political weapon); psychiatry in the Soviet Union (to which he draws some disturbing parallels in the United States); drugs (prohibitions against which are counterproductive); and sex (a fertile field for frauds, flakes, and fakers).

A staunch libertarian, Szasz is primarily concerned with the threat posed to the constitutional rights and responsibilities of Americans by the unholy alliance of government and the mental-health establishment.

Thus, a favorite target of his caustic criticism is the American Civil Liberties Union, which, in collaboration with ''experts'' on mental health, has worked to induce the US government to ship young Walter Polovchak back to the Soviet Union against his wishes.

Szasz also attacks the ACLU's policy statement regarding involuntary mental hospitalization as ''unqualified support of psychiatric slavery - of psychiatric defamation called 'diagnosis,' of psychiatric imprisonment called 'hospitalization,' and of psychiatric torture called 'treatment.' ''

The tone of Szasz's writing is often acidulous, bitter, supercilious, and seemingly devoid of compassion (as with his merciless condemnation of Patty Hearst).

He is smug, opinionated, and quite often right in what he says. That can be a difficult combination to digest.

Suffice it to say that Szasz writes to make one think, not to make one feel good.

Although his tone is responsible for his failure to provide the optimum possible rebuttal to mainstream psychiatry, anyone interested in mental-health theories still ought to read Szasz before formulating any fixed opinions on the subject.