TIDELAND
By Mitch Cullin.
192 pp. Chester Springs, Pa.:
Dufour Editions. $22.

BRANCHES
By Mitch Cullin.
Illustrated by
Ryuzo Kikushima.
197 pp. Sag Harbor, N.Y.:
The Permanent Press. $22.

The prose is a stage set for Cullin's ventriloquism, which is brilliant and beautiful: His 11-year-old wild child is identifiably such, with just enough sophistication in her voice and vocabulary to keep her from being too nave to be interesting. His middle-aged cop rambles through his noirish cantos and never utters a false-sounding phrase. Absent any real plots, both ''Tideland'' and ''Branches'' are suspended on their narrators' voices, which are story enough in themselves, rhythmic and telling as they recount the details of their days. ''Careful. Almost done,'' Jeliza-Rose says as she applies makeup in the empty house. ''Deadly lips as delicious as an apple. Dream Date Jeliza-Rose doll. When the lipstick reached the nooks of my mouth I had to pause; it was hard getting the scarlet neatly in the corners.'' ''I knew this boy / that made his mother laugh,'' Sheriff Branches says. ''Should've never bought him / that 9mm. / Should've bought him / a dog instead.'' You turn the pages just to keep them talking.

And if the talking gets them nowhere, it comes as considerable relief: a little misplaced sentimentality and both books would be worth much less. But they're a pair of small, hard pieces, like stones that you find in the bottom of your pockets -- which turn out to be gems, after all, albeit strangely faceted and a little bit dirty.