YOU ARE A WONDERFUL creature," Mark Twain once wrote to Helen Keller. "You and your other half together -- Miss Sullivan, I mean, for it took the pair of you to make a complete and perfect whole."

The "perfect whole" -- half Helen Keller/half Annie Sullivan, her teacher -- is the subject of this double biography which Joseph Lash, author of ELEANOR AND franklin, has written under the sponsorship of Radcliffe College.

Helen Keller's triumph over mulltiple afflictions -- blindness, deafness, speechlessness -- made her one of the wonders of the world. How the blind-deaf-mute girl was freed, through a miracle of education and self-will, from silent darkness to become a graduate of Radcliffe, writer and lecturer, is as familiar as a favorite bedtime story. Last retells it with new emphasis on Helen's intricate relationship with brilliant but prickly Annie Sullivan. Even his wordy rendition (811 pages, three pounds), freighted at times with inessential details, cannot flatten this most magical of tales.

It is difficult to think of a more symbiotic connection than the bond between Helen and the "Teacher" who revealed to her (in the famous scene at the water pump) the mystery of language -- that there are symbols, words, to express thoughts and feelings. For 49 years thereafter Annie described to Helen people, scenery, events, conversations, lectures, abstract ideas by spelling out the words in the palm of Helen's hand. Except for the things she could smell and feel, Helen's knowledge of the world beyond her silent "steel cell" was filtered through the brain and hand of Annie. Nowhere is the intriguing nature of their bond -- and Helen's handicap -- made more understandable than in the 61 photographs included in this book.

They were "one in two -- two in one" as Nelson Doubleday, Helen's publisher, later put it. A perfect fit of brilliant teacher, gifted student, each bound to the other by necessity. Annie made Helen's crippled life possible by acting as her other half; Helen made Annie's inner torments bearable by giving her uncritical love. When, at 21 Annie first met her 6-year-old pupil, she wrote, "I have found a real friend. One who will never get away from me, or try to, or want to."

As in most intimate, stable, longlasting collaborations, their was a match of opposites. Annie Sullivan, the product of a misshapen, brutal childhood was as difficult and doubting as Helen, who came from a gentle Southern background, was patient, affectionate and trusting. Annie's Dickersian beginnings are less well known, but equally unusual, and her own triumph over adversity was awesome. She was eight years old and half blind when she was abandoned by her drunken, abusive father to the Tewksbury, Massachusetts, poorhouse. (Her mother and two siblings had already died; her beloved little brother, jimmy, died in the poorhouse at her side.) For six lonely years she lived there, in the midst of chaos, ignorance and disease -- until she freed herself by sheer force of will. When a committee of Massachusetts grandees came to investigate the poorhouse, she threw herself at their leader crying, "I want to go to school!" He listened, and she was sent to the famous Perkins School for the Blind in Boston, where her powerful mind was liberated and some, but not all, of the rough edges polished down. She kept her early years a secret (even from Helen until they were both well past middle age) but it was a "secret" which spilled out in anger, depression and self-hatred throughout her life.

When Annie Sullivan first met young Helen on the front porch of the Keller house in 1887, Helen rushed at her with such force, she almost threw her to the ground. Their two lives were welded into one, and the rest is history. Annie first disciplined the "wild, destructive little animal" and then taught her the miracle of words -- which she learned with an explosion of understanding. Within five months she knew 575 words and within a year was ready for French and Latin. "The education of this child," wrote Annie, "will be the distinguishing event of my life."

From then on, the two were seldom apart for half a century. Given their intimacy and Annie's possessive personality, it was inevitable that the only real attempt to separate them failed. When Helen was 17 and being prepared for Radcliffe (too severely, Annie's detractors thought), the headmaster of the Cambridge School, with the help of Helen's mother, tried to part them. He was instantly defeated. "If I have to decide between my mother and Teacher," Helen pronounced, "I will stay with Teacher."

Helen spent four years at Radcliffe with Annie Sullivan at her side, summarizing lectures, translating classroom discussions, reading entire books into her hand. Equally intimate was their later collaboration on Helen's books. Helen wrote; Annie prodded, organized, edited and apparently added the touches of wit and color which mark Annie's own admirable writing. Lash examines some of the puzzles inherent in a partnership of such close harmony. Who was the genius -- Helen or Annie? The question has often been asked, but the most convincing answer here comes from John Macy, the editor and writer, who lived and worked with both women from 1905 (when he married Teacher) until 1914 (when he left her). Helen's "heart," he wrote, "is noble; the world has yet to see a finer spirit, a loftier and more steadfast will to do the best. . . . Her mind is stout and energetic, of solid endurance," but she is not a "brilliant genius." It was, he wrote, "Miss Sullivan's skill in presenting material," allowing it "to pass through her to the busy fingers of her pupil; her instinct in striking out the inessential; her feeling . . . for just the turn of thought that Miss Keller needs" that was remarkable. "Miss Sullivan has the knack of teaching." She was, he thought, "a genius."

Lash looks into the tricky matter of the "borrowings" in Helen's writings where whole passages and thoughts from other works turned up. So much of what she knew was "read" to her by other people, and her memory was so retentive that, as she wrote, "I cannot tell surely which of my ideas are borrowed feathers, except for those which I gather from books in raised print." The borrowing problem, which once brought a charge of plagiarism, troubled her so that she sometimes thought she should stop writing altogether.

Lash follows clues to another painful twist in the Helen/Annie knot. Did Annie Sullivan, abused as a child, in turn abuse young Helen, subject her to uncontrolled anger, the "silent" treatment, closing her only channel of cummunication? The possibility remains unproved but not unlikely.

Lash brings new insights to Helen Keller's life. But he also brings more than we want to know about the institutions which surrounded her, for example, the Socialist Party and the Industrial Workers of the World (which she joined) and the American Foundation for the Blind (which underwrote Helen and Annie in return for their work). But these are mis-steps in a long and interesting journey.

We all know the legendary Helen Keller. Lash has helped us rediscover Annie Sullivan, a difficult but fascinating woman, a teacher of enormous power, who added immeasurable dimension to Helen Keller's life. Just before she died in 1936 she said, "Thank God I gave up my life that Helen might live. God help her to live without me." Helen did live on -- for 32 years, but her life, and the telling of it here, lost much of its vividness and zest when Teacher left the scene. After she was gone, Helen, in her terrible grief wrote in her journal, "Every hour I long for the thousand bright signals from her vital beautiful hand. That was life!"