CHILDREN OF A LESSER GOD -- At the National through May 9.

The key speech in "Children of a Lesser God," the eloquent, prize-winning play at the National Theater, cannot be quoted because the words are unclear. Nor can it be paraphrased, because its meaning is too complex.

It's the climax of a fight between a deaf woman and her husband, a speech therapist. He had been dazzled by the proud defiance with which she refused to learn from him -- her insistence on being accepted on her own terms, and her refusal to attempt anything she would not be able to do well -- and their household is conducted in sign language. But in anger, he has taunted her to come into his world, because few people from the hearing world will bother to enter hers.

She replies with the first sounds he has heard her utter. The fury in her voice is clear, but the sound is harsh noise. The shock to them both is crushing.

As a teacher, he should be elated, because it's the crude beginning of speech; but as a husband, he shares her humiliation in her marred glamor. The position of each is still valid, but the human bond that prevailed over their differences may be shattered.

Mark Medoff's play, which won three Tony awards in New York, is as much about dependence as deafness. It has no easy answers, and it has no easy sentiments, either. You are not going to come out feeling good about having spent an evening sympathizing with the unfortunate, but you will find that you have acquired enough familiarity with the deaf to be as amused and as exasperated by their strengths and defenses as by those of the hearing characters.

The chief source of both interest and humor is how small the variations are between the flawed humanity of the deaf and that of the hearing -- how recognizable obscenities are when spoken with the hands, how similar the techniques of defiance and the accusations of egoism they make at each other.

The excellent cast, directed by Gordon Davidson, has deaf actors in the speaking and non-speaking parts of deaf characters, and Linda Bove is a compelling presence as the heroine. The set consists of benches and actors' imaginations.

But the play really belongs to Peter Evans in the role of the husband, who introduces the action in a narration and at once speaks his own role, delivers it in sign language; and speaks the part of the wife as he reads it from her sign language.

It's a particularly endearing character, as well as a strenuous one. His charm is not that he is good to the deaf, but that he is everything else with them -- mostly sexy and sarcastic. His wife is embarrassed because she doesn't talk? "I'll tell them that in a moment of erotic madness, I bit your tongue out of your mouth." He is as willing to attempt explaining the beauty of music as he is unwilling to accept his wife's receptivity to musical vibrations as anything approaching the true experience.

This is not an easy man to fell with the old radical insult that he is only trying to help others because he is trying to glorify himself. Not when he announces that no one can expect a person with his Peace Corps record to quit -- not after he "taught the Ecuadorians to grow and love brussels sprouts.