LINE 8-inch square pan with foil, with ends of foil extending over sides of pan. Beat margarine and peanut butter with electric mixer until blended. Add wafer crumbs; mix well. Gradually add sugar, mixing well after each addition. Press onto bottom of prepared pan.

MICROWAVE frozen whipped topping and chocolate in microwaveable bowl on HIGH 1 min.; stir. Microwave an additional 15 to 30 sec. or until chocolate is melted and mixture is blended; stir. Pour over peanut butter layer; spread to evenly cover peanut butter layer.

REFRIGERATE at least 2 hours. Use foil handles to lift dessert from pan before cutting to serve.