Margaret Atwood and the roots of defensiveness; Second Words: Selected Critical Prose, by Margaret Atwood. Boston: Beacon Press. 444 pp. $18.95 (hardback).

Margaret Atwood is always on the edge. She is the individual peering into the revolution or the wilderness or the disintegrating romance. Her characters need to view themselves as iconoclasts. Atwood as writer often assumes the role of moral witness or critic within the fiction and poetry. This detachment could be partly explained by her isolation as a child (she grew up six months of the year in the Quebec north woods, where her father was a forest entymologist); partly by her self-sufficient, reserved family; and partly by her early literary successes.

But this separateness is also a birthmark of her Canadian heritage. She stands on the sidelines, observing, meditating, judging, expounding. Long angered by the way Americans ostracized their northern neighbors, she has become a militant Canadian nationalist. Thus the work often portrays the me vs. them and the us vs. you dichotomies in her life. She is circumspect and tough, bravely confident and defensive. After years of being fascinated by these tensions, I yearn for a compassionate synthesis in Atwood's work. I often wonder if she is supercilious about community or simply diffident.

''Second Words'' is a map of Margaret Atwood's intellectual and aesthetic development, tracing her growth as a citizen of the city, the nation, and the world. The book opens a light on all her work, sharpening readers' appreciation of her fiction and poetry. It presents the scope of her vision, allowing us to understand more clearly her various voices as writer and narrator. These essays follow her from the University of Toronto, where she was an ethereal would-be intellectual who felt safest in the woods and the library; through her developing awareness as a female working in the world; as a Canadian nationalist; and as an activisit for such causes as Amnesty International. Her novels describe women learning from treacherous experiences and balancing on thin, parallel lines of cynicism and optimism.

Likewise, these essays are written in a distant voice, by a critic passionately concerned about the world, but somehow immune to it. The isolation is crucial for Atwood, guarding her from the rim, preserving her sanity. This is evident in the very tone of such essays as ''An End to Audience'': ''I have been asked here presumably because I am a storyteller and you wish to know something about the state of storytelling, either in this country or in this decade or both.'' Although she seems to have found her confidence on the margins, developed her edge, if you will, I wonder if this role of moral ringmaster will not result in self-parody after a while. At the age of 45, with five novels and over a dozen poetry collections behind her, she is perhaps the most gifted Anglophone writer of her generation. Still, all authors reconsider direction at some point in their careers.

Here, as in all her work, she is a spare, intelligent, ironic woman who writes with verve and control and an almost breathless confidence. This expository writing is distinguished from her other work by a striking line between the telling (in her essays) and the revealing (in her art). Her novels have significant emotional depth, which is the power of a passionate unconscious. Since she lacks a certain ability to analyze psychologically in her criticism, however, the essays sometimes emerge as stark and defensive. Perhaps the fiction is more accessible because she exposes parts of herself in the characters, while in the essays she has created a wry, aloof character named Margaret to protect her from the world.

''Second Words'' is divided into three sections. Part I contains the essays from 1960 to 1971, describing her gradual emergence from academic confinement into heated nationalist politics. Part II, 1972-76, is more about women, asserting her determined autonomy while taking assorted potshots at the feminist movement. During this phase, she became a literary diplomat, writing reviews of Canadian books for US papers and of American books for Canadian journals. In the third section, 1977-82, she covers similar themes from a more global perspective.

The first section will be of sharpest interest to Canadians and to those outsiders who have already had the pleasure of becoming acquainted with versatile Canadian literature. Here are reviews of Gwendolyn MacEwen, Al Purdy, George Jonas, and other fascinating writers. Atwood begins to find her own pace in the essay ''Nationalism, Limbo and the Canadian Club,'' in which she explores and explodes her own profound Canadian identity. Reflecting back on a stifled 1950s childhood, she writes, ''Canada was for us not-America, the place where popsicle bag offers didn't apply and everything was 10 cents extra; the comics were news bulletins of the action going on across the border which we could watch but not join.'' In 1972 Atwood published a stunning book of criticism, ''Survival: A Thematic Guide to Canadian Literature,'' which added sparks to the already incendiary debate about cultural nationalism. The essays in this section describe the period's political pyrotechnics as well as Atwood's personal reunion with Canada. Until the early 1970s Canadian literature was ignored in Canadian universities, especially in departments run by immigrant American and British professors. In 1974, 95 percent of the books sold in Canada were written by foreigners. By trying to recover Canadian literature, analyze it, and promote it as art, Atwood took a big risk. As a young poet she might appear too academic in her literary criticism, too polemical in her convictions, and, not least, too self-serving in her promotion of indigenous literature. ''Refusing to acknowledge where you came from ... is an act of amputation: you may become free floating, a citizen of the world (and in what other country is that an ambition?) but at the cost of arms, legs, or heart. By discovering your place you discover yourself.''

Although Atwood begins to argue vociferously for the artist's connection with society, she still maintains her distance from issues. Society becomes more and more her subject matter, yet somehow she is not subject to society. Although she writes as a socialist, she eschews any serious interpretation of class. And she insists on referring to the ''writer'' as ''he'' or to the ''reader'' as ''he.''

Atwood's rigid resistance to feminism is the most startling aspect of the book for me. While she ardently promotes female strength and independence in such essays as ''A Harvest Yet to Reap: A History of Prairie Women,'' ''Witches, '' and ''On Being a Woman Writer,'' she continually disavows any ''official'' connection with feminists. At first she voices genuine disagreement with certain women's movement ideas. As her thinking gradually incorporates a feminist perspective, however, she seems to panic about being swallowed up, about losing not only her identity as an iconoclast, but also her privilege and safety as the woman on the edge.

Her early statements betray an almost McCarthyesque paranoia about being identified as a fellow traveler. In 1976, she writes, ''I can think of only one writer I know who has any formal connection with any of the diverse organizations usually lumped together under the titles Women's Liberation or the Women's Movement.'' I find this particularly odd, because I remember several writers Atwood knew at the time who were active feminists. Her strident denial is embarrassing. What is the root of this defensiveness? Does the ''community'' of feminists undermine her self-image as an intellectual hermit digging new ground, courageous and alone?

Part III offers reviews of other women writers, Tillie Olsen, Pat Lowther, Nadine Gordimer, Sylvia Plath. Her essay about Mary Helen Washington's visionary anthology of black women writers, ''Midnight Birds,'' is thoughtful and enthusiastic. But I am troubled by her eager identification with black writers - as a Canadian who has also suffered the indignities of American imperialism! Her ready empathy seems exaggerated, coming from a highly schooled white. And her sincerity is undercut by the misspellings of the names of the editor and one of the contributors. Perhaps the most delightful parts of this section are her appreciations of her former professor, Northrop Frye, and of her Connecticut ancestor, who walked away after being hanged as a witch: ''If there's one thing I hope I inherited from her, it's her neck.''

The publication of ''Second Words'' establishes critical patterns through which a provocative, original mind interprets the world. Thus it helps us to reassess all her work. Sometimes her poems and novels seem like intellectual games in which she sets a solitary figure through a puzzle while carefully outlining the predetermined rules for her audience. She is better at monologue than at dialogue, leaving little room in the text for argument. Developing a dialectic in which readers engage in real choices would diminish her control. Yet I see this as the risk Atwood needs to take now.

In ''Life Before Man,'' she draws a map of progress: ''On her wall the tree of evolution branches like coral toward the ceiling: Fishes, Amphibians, Therapsids, Thecondonts, Arcosaurs, Pterosaurs. Bird, Mammals and Man, a mere dot. And herself another, within another. Which will exfoliate in its turn.'' Perhaps it's not so much a question of evolving from each other as of evolving with each other. Perhaps Atwood needs to be assured that moving from the edge does not mean falling into the void. By linking with an imaginative collectivity of writers and readers, she might find that strength is neither best initiated nor best practiced in isolation.