SARTON SELECTED: An Anthology of the Journals, Novels, and Poems of May Sarton (W. W. Norton: $22.95; 307 pp.). Of course no one knows how to die. "After all," Sarton explains, "we meet every great experience in ignorance--being born, falling in love, bearing a first child--always there is terror first." In her novella, "As We Are Now," she has taken a subject no one wants to think about, being elderly and abandoned to a substandard nursing home, and made it a gripping, powerful tale. Old age is a place where escape fantasies have only one practical form: death. In another section, Sarton describes her childhood, giving life to a particular aunt who was joyously difficult and intensely alive. In her comments on poetry, she states that "beginners are narcissistic and conservative" and therefore unwilling to break down and explore their own poetry and re-create it until it is worthwhile.