UNDER THE NEEM TREE by Susan Lowerre (Permanent Press: $21.95; 255 pp.). It sounds close to hellish--spending two years in a tiny Senegalese village at the edge of the desertified African Sahel, trying to manage a fish farm in which the native population takes little interest. Susan Lowerre was 23 when she joined the Peace Corps in the mid-1980s, and it's a good bet that only youthful idealism saw her through. Regularly incapacitated by parasites, constantly frustrated by both her work and her workers, and sometimes despised for her femininity and her white skin, Lowerre had all kinds of reasons to pack up and leave. But she didn't--and that turns out to be a victory in and of itself, for at bottom "Under the Neem Tree" is about simple survival. Lowerre's prose is flat and her observations almost adolescently self-absorbed; even so, the book is memorable. The author isn't afraid of being thought naive, impatient and sentimental. Lowerre writes at one point that she refused to wash her sweats because they smelled of her mother's fabric softener, but given how little personal history she was able to hang on to in Senegal, the sappy admission rings true.