In the latest episode of a yearlong feud that has transformed the Spoleto Festival U.S.A. into something of a soap opera, Gian Carlo Menotti, the festival's 79-year-old founder, said yesterday that he would not return to Charleston, S.C., next year unless the festival's top officers resigned.

The general manager, Nigel Redden, and the two board members, Ross A. Markwardt, chairman, and Edgar F. Daniels, president, repeated what they had been saying since Menotti first threatened to leave the festival last October: that they recognized Menotti's prerogatives as artistic director, that they had never challenged them and that they did not understand why he had publicly painted them as villains.

Menotti met yesterday with Charleston Mayor Joseph P. Riley, to enlist the mayor's aid in the battle. And Riley, a supporter of Menotti, has imposed an uneasy truce, which he said he expected to last until the festival ended on June 9.

"No change of leadership is going to occur now or during the rest of the festival," Riley said. "I see this as a family argument, something we will work out when the festival is over."

Neither Menotti nor the mayor would enumerate the grievances.