One of the most compelling protagonists in contemporary fiction is the bright adolescent girl, her observations of human nature made keen by inherent self-consciousness and candor. This is the typical heroine in Orringer's fine book of stories. Themes of ill mothers, Judaism, and New Orleans (the author's hometown) run through the wry, poignant collection, whose plainly stated physical details are often emotionally evocative: ''I have to run through the snow to catch the bus, and along the way my shoe comes off and I take one cold wet step. Everyone finds this hilarious, even the bus driver.'' In ''Note to Sixth-Grade Self,'' a girl ostracized by the class clique fleetingly believes the cute boy likes her. ''For this one moment,'' Orringer writes, ''you have no hangnails, no bony knees.'' Such clear-eyed precision makes Orringer's debut as heartbreaking as it is clever.