Heat rice, water, and 1/2 teaspoon salt to boiling in small saucepan; reduce heat and simmer, covered, until rice is tender, 45 to 50 minutes. Drain, if necessary, and cool.
Mix milk, margarine, egg, egg whites, and rice. Add combined all-purpose and whole wheat flour, baking powder, sugar and remaining 1/2 teaspoon salt, mixing just until dry ingredients are moistened.
Spoon batter into 12 greased muffin cups.
Bake at 400 degrees until muffins are browned, 20 to 25 minutes.