A look at mural art of the '30s; Wall to Wall America, by Karal Ann Marling. Minneapolis: University of Minnesota Press. 348 pp. Hard cover, $35. Paperback, $14.95.

When Stefan Hirsch painted a mural depicting ''Justice as Protector and Avenger'' in the Aiken, S.C., courthouse, he had no idea the trouble he was stirring up.

It seems the folks in this depression-era town - who had never been consulted about the painting - thought the shadowy female image of justice looked like a mulatto. Such were the hazards, it seems, of a controversial New Deal program that often pitted ''outside'' artists against local tastes and preferences.

Between 1934 and 1941, more than 1,100 murals were commissioned for the walls of courthouses and post offices under the auspices of the Treasury Department Section of Fine Arts. Author Marling uses these paintings to examine the popular culture of that turbulent era, exposing the dense mesh of conflicting interests exposed during this experiment in government-supported art.