'Extraordinary eloquence'; Children of a Lesser God. Play by Mark Medoff. Directed by Gordon Davidson.

Instructive plays are not your everyday Broadway fare. Nor are plays that seek to view with sensitivity and insight the particular problems of a handicapped minority. Score two points, then, for Mark Medoff's "Children of a Lesser God." The new romantic comedy drama at the Longacre Theater can claim one additional distinction: Since it involves the running use of the sign language of the deaf, it is a work of extraordinary visual eloquence.

"Children of a Lesser God" concerns the relations between staff and students at a school for the deaf. Speech therapist James Leeds (John Rubinstein), a Peace Corps alumnus, woos and marries Sarah Norman (Phyllis Frelich), a non-hearing maid and student. Sarah defiantly prefers her mops and pails to the prospects of self-improvement open to her if she would let James teach her to speak and would admit her proficiency at lip-reading.

Although the marriage starts off reasonably well, the fundamental impasse between Sarah and James persists. She becomes expert with a microwave oven and a blender, drives a car, and plays a dazzling first game of bridge. She insists that James's classical recordings mean something to her vibrationally. But notwithstanding her husband's helpful role as sign-language translator (a fascinating feature of the production), their relationship grows increasingly strained.

The final confrontation occurs when one of the students enlists Sarah in an appeal to the civil rights commission concerning the school's discriminatory practices against those it is designed to help. Sarah rejects the intervention of a well- meaning woman attorney and insists she will deliver her own speech in sign language. The appeal succeeds but the marriage founders -- whether beyond rescue is left uncertain.

"Children of a Lesser God" is funny, touching, and at times dramatically tense. Its weakness theatrically derives from the casualness with which Mr. Medoff treats certain secondary details (notably the preparation of the protest effort) and incidental characters, who are scarcely more than props for the plot. Like such plays as "Whose Life Is It Anyway?" and "The Elephant Man," "Children of a Lesser God" is not merely about the plight of physical impairment. It is about the human condition and the struggle to communicate across daunting barriers. Mr. Rubinstein plays leads with compassion, humor, and dedication. Since Miss Frelich speaks but once in the play, his role is not only that of translator but interpreter.Miss Frelich, co-founder of the National Theatre of the Deaf, gives a performance of great emotional intensity and drive. Without spoken words, she articulates eloquently Sasrah's pride and determination.

The cast directed by Gordon Davidson includes Lewis Merkin, William Frankfather, Scotty Bloch, Julianne Gold, and Lucy Martin. Thomas A. Walsh's functionally simple setting requires imaginative playing as the action moves cinematically in and around the school. Nancy Potts designed the costumes and the lighting is by Tharon Musser. "Children of a Lesser God" was originally produced by the Center Theatre Group/Mark Taper Forum in Los Angeles.