William Gibson's tough and fine play about the education of Helen Keller, "The Miracle Worker," is being expertly performed at Olney Theatre. You may think it awful to drag yourself out in the heat to watch something terribly worthy when you could be enjoying a rousing summer musical instead, but this has the bracing effect of a sharp tonic instead of the usual lemonade.

The play concerns the first breakthrough Annie Sullivan made in teaching discipline and the concept of language to a deaf and blind child who had been allowed by an indulgent family to run wild. At the end of the play, pupil and teacher are both disheveled and exhausted - and so are those members of the audience who cry messily - and the result is simply that Helen Keller associates the word "water" with what is coming out of the pump. It is enough of a miracle without our knowing that Helen Keller was to go on to graduate from Radcliffe and, among other accomplishments, learn Greek.

The most compelling scene is silent except for the clattering of plates and chairs, as two strong-willed individuals fight out whether Helen should have to take on the rigors of learning or be excused by pity. In this time of civil-rights struggles by the disabled, the message that pity is a worthless stumbling block on the road to independence is stunningly made. The untamed and spoiled Helen is repulsive as she grabs food from others' plates to stuff into her mouth; but her beauty when she is given the tools with which to express her humanity is dazzling.

But wider points are made than that. In the nearly 20 years since "The Miracle Worker" won the Tony award for best play, the culture has been inundated with the panaceas of "love" and "communication." Annie keeps making the point that love has handicapped Helen with its tolerance; that what is needed is a highly demanding intolerance. Annie's faith, as a teacher, is in language - Helen has had no trouble expressing her feelings, with kicking and biting. What she needs are words.

Theresa Ann Karanik's Helen is her professional debut, and it's a performance of such skill that you can hardly recognize her when she apperars in the curtain call, with the eyes and the stride of a normal young woman. Pat Karpen, too, is excellent as the gutsy young teacher who, when anyone else would flee, reminds the unhearing Helen that she has nowhere else to go.It is only a small shame that the urchin humor she brings to her opening scenes gets somewhat smothered as the action gets rougher.