One girl's battle against the Klan; Morning Glory Afternoon, by Irene Bennett Brown. New York: Atheneum. $9.95.

Irene Bennett Brown has crafted an old-fashioned story for girls -- but one with a currently important theme. The time is 1924; the place, a small Kansas town, apparently peaceful.

Into this setting arrives 17-year-old Jessamyn Faber, escaping from painful memories of a boyfriend's drowning, a death for which she feels responsible. In Ardensville, Kan., she finds a job as the town's only telephone operator. Jessy soon realizes she is expected to be a town crier and fount of information: to know the recipe for watermelon preserves, if the local train is on time, and the current price of feed. Though the townspeople treat her impersonally, calling her Central (for Central Switchboard), she becomes the hub of that town's life.

Lonely for her young sisters back home, Jessy befriends two orphaned, immigrant girls who live with their brothers in an abandoned coal shack outside of town. When the children start having problems -- a fire, threatening notes -- Jessy assumes that these are just local children playing pranks.

Then other incidents occur. A child is "misplaced" and returned. A rock is tossed through a store window. In each case, the victim is "different" in some way -- a black, a Greek, a Jew, or a Roman Catholic. Soon a pattern begins to emerge. And at Central Jessy picks up clues about who's to blame -- the town's suave and popular mayor, Lombard Hale.

Jessy's best friend, Lilli Miller, sees the influence of the Ku Klux Klan behind these incidents, and she wants to stop it. But how? The mayor is too deeply entrenched, and he plays too successfully upon people's fears.

At first, Lilli and Jessy take ineffectual stands against the mayor. Their horror builds, as hooded Klan members terrorize innocent children in a Christmas play, driving off those who are "different," while the audience remains frozen.

We feel Jessy and Lilli's helplessness. They want to stop the scene, to blot it out, but they are paralyzed by fear. We particularly sense Jessy's vulnerability. She is the morning glory of the title, displaying her petals only in the quiet hours of the day but closing them when the sun gets too hot.

Finally, Jessy discovers a way to defeat the mayor and his followers. She also learns that many townspeople have come to respect and depend upon her. She finds love, a place in this town, and the strength to face her own problems.

The author successfully depicts Lombard Hale's slick, polished mannerisms and underlying nastiness. The mayor obsessed with neatness, gleefully pounces upon litter, both paper and human. In his warped mind, removing clutter includes eliminating "unwanted" people. He is a vicious adversary who cleverly manipulates events.

The novel has weaknesses as well as merits. In the beginning it comes dangerously close to moralizing, but fortunately this tone soon disappears. The pace is sometimes slow, and the wonderful descriptions of life as a village telephone operator would have been better told in direct quotes.

At a time when the Ku Klux Klan is making news again, the book's message seems especially relevant. It throws light on such questions as why people hate those different from themselves, and why individuals are s ometimes attracted to organizations like the Klan.