The long arm of coincidence.

In Another Country, by Susan Kenney. New York: The Viking Press. 163 pp. $13. 95.

Sara, the narrator of this excellent first novel, is told by her father before he leaves on a business trip, ''See you later ... you take care of everybody now.''

Her father dies on that trip. Sara is 12 at the time, and his death produces her ''rescuer complex.'' ''Ever since my father died,'' she reflects as an adult , ''I have felt that it was my responsibility to keep everyone around me safe. This has meant saving them when necessary, at the very least hovering somewhat officiously, a walking first-aid manual, rapid extricator and rehabilitator of lost causes. ... I can't help believing deep down that whatever is lost can be recovered, what is broken can be mended, and what is gone replaced; at least it's worth a try.''

There are plenty of people in her life to take care of: a mother who goes crazy, her younger sister and brother, and then her own children and a dying husband. There's even an injured dog.

''In Another Country'' at first seems more a collection of short stories than a novel; ''Facing Front,'' the center chapter, won the O. Henry Award in 1982. This technique can disappoint a reader if a strong, sustained narrative doesn't soon develop. But in this book - as in Pat Barker's ''Union Street,'' an English first novel about seven North Country women living on the street which unites them - a jigsaw-puzzle effect is created, the necessary narrative emerges, and the result is greatly satisfying.

''Facing Front'' concentrates on the madness of Sara's mother and will especially move those readers who have themselves coped with so-called ''crazy mothers.'' When the ''Ruth's Song'' chapter of Gloria Steinem's ''Outrageous Acts and Everyday Rebellions'' was published in Ms. Magazine, describing her years with a mother who was fed knockout drops by doctors, the magazine received a ton of mail from women telling their own tales of mothers who retreated from wife-and-mother expectations and responsibilities into worlds of their own.

''She is our mother,'' Sara's sister says. ''Always and forever our mother. Even if she is crazy.'' Over the years Sara's emotions shoot back and forth: anger, pity, forgiveness, love, anger again. Her fear of becoming like her mother intensifies when her husband falls ill: ''I'm not my mother, I think, I'm myself, I'm different, and I don't have to run ... away from that unfaceable fact of death.''

When the reader learns that Sara's husband may be dying, the long arm of coincidence begins to resemble Plastic Man's. As her husband says, ''This is the worst thing I could have done to you,'' and Sara knows ''that he is thinking about my father's death.'' Yet any objections to the coincidence are quickly dismissed in the unfolding of some magnificent writing about death. It is dry-eyed writing, but its effects are a lump in the throat and a dash for Kleenex.

''In Another Country'' is altogether a beautiful book.