WHEN THE BOMB DROPS, a woman will watch from the banks of the Potomac, recording the colors of the clouds after the first blinding flash. She is Linda Pastan, author of five poetry collections including the new PM:AM: New and Selected Poems.

Artists of every generation have had to deal with the fear that theirs is the last to walk the earth. There days, fear of extinction seems increasingly rational. It's no accident that much of contemporary writing is obsessed with survival, and poetry is increasingly morbid. Women poets in particular face a struggle for acceptance along with the panic of modern life. One way out of the death trap, suicide, seems at the very least impractical.

Pastan's poems take the other exit, searching for hope and continuity among the remnants of more joyous times. She seeks strength in the multitude of roles a person plays as social relationships grow more complex, and her poems find solace for most woes in mathematics, astronomy, gynecology, and other surprising images.

By exploring in depth some of the social roles--mother, tourist, Jew--she has accepted. Pastan gives her writing the special vitality that comes only from external matter. The poems in PM:AM are always reaching out beyond conventional scope, grabbing onto things that exist wholly apart from the poet and her realm of existence.

In "Drift," Pastan compares the movement of two sleepy lovers to the phenomenon of continental drift. A scientist would mumble about geology to explain a concept that always shocks people the first time they hear it. Conventional approaches to everything are dissolving, information is exploding, and the earth's very continents are slowly moving apart. Pastan dismisses the scientist's wishy-washy explanations simply: "It is natural law this drift."

One of the roles Pastan is not so matter-of-fact about is one we all must play at some point: the role of survivor. People are a source of life in Pastan's poetry--her children, her husband/lover, herself. When someone dies, her sense of creativity utters a gasp apart from mourning; its food has been wrenched away. But Pastan remains clam about the way life seems to decay after the death of a loved one. With the lines: The world is shedding - its thousand skins. she survives a funeral by noticing how mourners see the whole world as dry and falling down like an autumn day.

IN HER SEARCH for continuity to escape shock. Pastan goes back through Biblical legend tracing Judaic myth and history. Her idea is not to create an identity for herself but rather to find a universal past or one that can be shared with at least other Jews. In a poem somewhat formidably titled "A Short History of Judaic thought in the Twentieth Century," the poet scratches her bead at the intellectual custom of answering a question with a question. If it is forbidden to touch a dying person except to remove him from a burning house. Pastan asks, who can she touch' She writes: aren't we all dying' You smile your negotiation smile and ask but aren't all our houses burning?

Pastan's language is simple even spare. Usually it lends itself well to her subjects-- with complicated imaged and twists of thought there is no need for flowery language. But every so often a poem is skimpy. Because Pastan's only point of view is the poet looking out the voice dues not shift. The only source of excitement is what she sees. When the language becomes too terse, a poem might flop unless read very slowly. Fortunately, there are not many of these.

Twenty years ago, it looked as if there was little hope for a women poets. There were too many obstacles - ranging from rejection of female ideas by an audience unused to them to the observation with suicide that many women poets seem to have. A few contemporary poets - notably Mazine Kumnin and Denise Levertov - have overcome these problems. By Confronting the creative struggle head on without becoming obsessed Linda Pastan joints their ranks.