New collections reveal literary development of poets Plath and Sexton; The Collected Poems of Sylvia Plath. New York: Harper & Row. 288 pp. $15.95 in hard cover, $6.95 in paperback. The Complete Poems, by Anne Sexton. Boston: Houghton Mifflin Company. 622 pp. $ 20.

Sylvia Plath and Anne Sexton shared some ordinary and extraordinary distinctions: Both had roots in New England, studying for a time in the same writing class at Boston University. Both were poets who received a good deal of public and critical attention at a time when few women writers could usher their work into print. Both could be considered poets of the ''confessional school'' (after Robert Lowell and W. D. Snodgrass), and each startled the reading public with the vivid images of a woman's personal experience.

The saddest distinction these women had in common was a depressive and self-destructive energy which brought their voices and their lives to early and tragic conclusions. Somehow it was their dark visions and their deaths that snared the public's imagination, fueled feminists' battle cries, and elevated these women to a status approaching literary sainthood. All this obscured the most vital contributions of their lives: the poetic work they had wished to share.

Now, with publication of ''The Collected Poems'' of Plath and ''The Complete Poems'' of Sexton, readers have an opportunity to examine the full range of their verse and to know the writers behind the much-debated myths.

Sylvia Plath's ''Collected Poems'' contains some surprising revelations for both her readers and scholars. Ted Hughes, the British poet who was married to Plath, has done a meticulous job in editing and notating this collection. Since almost all of Plath's poems, with the lone exception of the book ''The Colossus, '' were published posthumously, the selection and arrangement of the work was somewhat arbitrary. To offer a truer picture of her development, Mr. Hughes has set the ''Collected Poems'' chronologically. We can now read through the manuscript as it grew, new entries arriving each week, each day, or even several in a day during the white-hot creative rush in her last year.

The result is something like those time-lapse botany films that show us a seed sprouting, growing, and flowering all in 10 minutes' time. From her ''Colossus'' poems to the furious output of 1962-63, we witness all the growth stages of an individual's creativity compressed into a mere seven years.

The very early poems are unremarkable but finely crafted. Plath mastered the technical intricacies of poetry simply for the challenge and the pleasure of it; mannered and reserved, her poems still clearly display her passion for language and form.

As the emotional pressure in her life mounts, she begins to wrestle with her self-imposed limits, striking out with a new voice and a more personal poetic stance. Midway in this collection, the writing becomes finally liberated of any restraints. She seems to have stopped writing to please her male counterparts and teachers. The craft is not abandoned but set to new purpose; she adds to it a ferocious honesty, and an inventiveness for language and imagery that gives the scenes of her life a haunting quality. In ''Magi,'' faceless spirits, with their abstract concepts and philosophy, hover over the cradle of a girl-child. But for the baby, the heavy notion of Evil attending her cot is less than a belly ache and Love the mother of milk, no theory They mistake their star, these papery godfolk. They want the crib of some lamp-headed Plato. Let them astound his heart with their merit. What girl ever flourished in such company?

If some readers find the material from this period too dark and serious, they might consider that, in the context of her life, the poems also exhibit the astonishing quality of the human spirit countering grief with the clarity of thought and the desire to create. This book refutes the public's romanticized view of the ''mad genius.'' The artist revealed here is a superbly skilled craftswoman, struggling to bring her deepest perceptions into language. Plath's poetic powers were fully freed by the time of her death, and we can only guess at the dimensions her work might have reached.

Perhaps Anne Sexton's is an even sadder story, because the high point of her work occurred earlier in her career, and the later poetry became overextended, desperate with the need to reach out for help. She was almost 30 years old before she turned to the writing of poems. When her pent-up energies finally burst free, Sexton began writing some of the strongest, most intimate feminist poetry ever produced. Her early books were favorably received, and many women readers identified strongly with the honesty of her voice and the severity of her experience. But, while this public performance of personal pain gave her the attention and support she needed, she outraged as many readers as she pleased.

Now, almost a decade after her death, much of the controversial material in these pages is considerably less shocking but also less vital to new readers. There are several poems in each collection and isolated moments in many of her lyrics that are awesome in their depth and vitality, but as you read through ''Complete Poems,'' too many pieces are overlong and unfocused, crammed to the bursting point with wild words, personal icons, and random strikes at self-definition.

Taken together, the works of Plath and Sexton provide a devastating commentary on the reader's world as well as their own. Why did women writers have to batter their way into the literary marketplace? Why is it that the suffering and the fatalism of their poetry drew more reader response than the art of their writing? At the time of these two much-publicized deaths, suicide became something of a vogue many writers flirted with, as if that somehow added the stamp of authenticity to their work. These books are powerful reminders of what is lost when society idolizes its dead poets and ignores the living.