A tentative agreement was reached on a dispute that has almost stopped production at Fiat, Italy's largest private employer. In announcing the accord, Labor Minister Franco Foschi said all sides had made compromises. Details of the agreement were not disclosed. Negotiations began about a month ago after Fiat proposed laying off 22,884 car workers because of a slump in foreign sales. The Metalworkers' Union, fearing the layoffs could become permanent dismissals, picketed most of Fiat's plants.