Biography promises much -- but raises doubts; Marie: A True Story, by Peter Maas. New York: Random House. 417 pp. $16.95.

When Marie Ragghianti was chairwoman of the Tennessee Board of Pardons and Paroles, she blew the whistle on corruption. It cost several people their jobs and political futures, and sent them to prison. A few key witnesses were found murdered. It was not an easy atmosphere in which to be stubborn and brave.

Instead of praise, she endured slander, threats, and eventual firing (though she won a lawsuit reinstating her). Once she said it was not ''the worst thing'' that ever happened to her. The worst was earlier - being a battered wife, raising her three children alone, and eventually working her way through college.

The trouble with ''Marie: A True Story,'' is that Peter Maas does not tell it as the investigative reporter he is (he wrote for leading magazines and is the author of ''Serpico''). Instead, he uses the docudrama technique, replete with re-created dialogue and an appalling lack of objectivity.

His attempts to deal openly with the flaws of his heroine (a legitimate charge for drunken driving, for instance) appear as pathetic rationalizations. The effect is to raise doubts rather than quell them.

His partiality takes on the tone of revenge. The raw language, petty gossip, and snide characterizations of those who oppose Ms. Ragghianti make the reader want to cry ''foul.'' Such savaging does not serve her cause, nor is it necessary. Maas has forgotten an important rule of journalism - just give the facts, and let their weight bring down guilty people or institutions.

Another rule: The writer cannot presume to say what is in the mind of the person he or she is interviewing. Maas makes such surmises throughout. Further, we have few direct quotations from the 76 people he interviewed and only fragments of the documents he studied.

Sadly, Ms. Ragghianti comes through as erratic, a description she would abhor but one the book's unevenness forces on the reader. Undoubtedly ''Marie'' will be filmed. Perhaps then we will see a less adoring but more believable portrayal of the local beauty queen who grows up under personal and political fire - and a more evenhanded, and thus tougher, treatment of her enemies.