One of childhood's more sobering initiations comes with the discovery that Barbie's head pops off, she'll never wear flats, and her boyfriend is a eunuch. A collection of poems and stories, Mondo Barbie dramatizes the lasting impression this Lilliputian bombshell has made on post-boom generations. In A.M. Homes' sidesplitting ''A Real Doll,'' a boy lusts after his sister's fully animated Barbie; John Varley's ''The Barbie Murders'' features a futuristic colony of ghoulish Barbie look-alikes; Rebecca Brown outs Barbie; and Gregg Shapiro dresses like her. Considering its plastic catalyst, this is an imaginative and curiously touching anthology. A-

