Pat the halibut steaks dry and place them in the crock pot. In a small bowl, combine the flour, sugar and salt. In a sauce pan, melt the butter and stir in the flour mixture. When well blended, add the wine and milk and cook over a medium heat until thickened, stirring constantly. Allow the sauce to boil for 1 minute while stirring. Pour the sauce over the fish and cook on high for 2-3 hours. Garnish with lemon wedges.