In a written statement, Arthur Ney, the Hamilton County prosecutor who convened the grand jury that indicted the museum, said that because of the dispute over the exhibition, ''the only alternative was to let those without an interest in the controversy make the final decision,'' adding, ''Whether you agree with the verdict or not, the final analysis is that the system works.''

Helms Keeps Banner High

The verdict ends seven months of turmoil in this quiet, conservative city on the Ohio River. After weeks of urging the museum not to display the photographs, Cincinnati law enforcement officials entered the Arts Center on the exhibition's opening day, April 7, and handed the indictment to Mr. Barrie.

Much of the dispute over the Mapplethorpe photographs has centered on whether Federal money should be used to finance them, through the National Endowment for the Arts. Senator Jesse Helms, a North Carolina Republican, has led efforts to keep endowment money from being granted to artists whose work may be considered by some to be obscene or sacrilegious.

Today Senator Helms said in a statement: ''This merely proves my point that taxpayers' money should not be used to subsidize filthy and offensive art in any form. The N.E.A., and others who have no concern about the effect of such subsidies, insist that the taxpayers' objections should be ignored.''

A Helms aide explained that the Senator believed the N.E.A. grant that helped establish the Mapplethorpe exhibition last year - but not its showing in Cincinnati - had, in effect, transformed the photographs into Government-approved art, making it impossible for a jury to declare them obscene.

The case centered on seven out of 175 photographs in an exhibition that traveled from Berkeley, Calif., to Boston without incident except in Cincinnati.

Five of the seven photographs depicted men in sadomasochistic poses and were the basis of charges that the museum and Mr. Barrie had pandered obscenity. Two of the photographs showed children with their genitals exposed and were the basis of charges the defendants had illegally displayed the images of nude children.