Preheat oven to 350ºF. Line 13x9-inch baking pan with foil, with ends of foil extending over sides of pan. Mix oats, 1/2 cup of the sugar and the margarine. Press onto bottom of prepared pan. Bake 10 min. Cool. Meanwhile, beat cream cheese, 1/4 cup of the remaining sugar and the milk with electric mixer until well blended. Stir in whipped topping; cover. Refrigerate until ready to use.