Place 1/2 cup warm water in large warm bowl. Sprinkle in yeast; stir until dissolved. Add remaining water, sugar, salt, butter, and 2 cups flour; blend well. Stir in eggs, mashed potatoes, raisins, and enough remaining flour to make soft dough. Knead on lightly floured surface until smooth and elastic, about 6 to 8 minutes. Place in greased bowl, turning to grease top. Cover; let rise in warm, draft-free place until doubled in size, about 1 hour.
Punch dough down. Remove dough to lightly floured surface; divide in half. Roll each half to 12 x 7-inch rectangle. Beginning at short end of each, roll up tightly as for jelly roll. Pinch seams and ends to seal. Place, seam sides down, in 2 greased 8-1/2 x 4-1/2-inch loaf pans. Cover; let rise in warm, draft-free place until doubled in size, about 1 hour.
Bake at 350°F for 35 minutes or until done. (Cover with foil during last 10 minutes of baking if bread is getting too brown.) Remove from pans; let cool on wire racks.
*Use water reserved from boiling potatoes or tap water.
**To use instant potatoes: Stir together 1/3 cup boiling water and 1/4 cup instant potato flakes or buds. Let cool to room temperature.