AFTER A two-week trial, a jury took less than two hours to acquit Cincinnati's Contemporary Arts Center and its director, Dennis Barrie, of charges that they pandered to obscenity and violated a state law against displaying pictures of nude children. At issue were seven photographs by the late Robert Mapplethorpe, which were part of a show at the CAC last spring. The prosecution is believed to be the first of an art gallery or museum on obscenity charges.

The Mapplethorpe show has been controversial everywhere. It was canceled by the Corcoran Gallery here and has been the subject of much debate in each of the five cities where it has been on view. The argument has focused, until Cincinnati, on the question of federal funding. Before this trial there had been no talk of arresting museum officials and subjecting them to possible prison terms. Indeed, Mr. Barrie and his colleagues had sought to accommodate those who objected to some of the material: only people over 18 were allowed to view the exhibit, and the most explicit photographs were shown only in a separate room. The indictment of the museum and the director -- and, of course, the sheriff's raid that followed -- came as a shock.

None of the eight jurors, self-described working-class churchgoers, was particularly interested in art. Yet the ease with which they rejected the government's case demonstrated that they understood very well what was at stake. The jurors simply wouldn't allow the government to decide what kind of art adults are allowed to see. The verdict is a rejection of police monitoring of the arts and of prosecutors who go after curators because of disagreements over artistic merit.

The struggle between artists and censors is an old one, and the forces of tolerance don't always win. Recently, for example, there have been successful criminal prosecutions -- one was later reversed -- in three southern states in connection with the sale of recordings by a rap group. But in Cincinnati, eight men and women stood up to the censors and affirmed the right not only of artists to create and display their work but of individual citizens to see that work and make up their own minds about it. The verdict is an important victory for free expression.