MIX wafer crumbs, peanuts, granulated sugar and margarine. Remove 2 Tbsp. of the crumb mixture; set aside. Press remaining crumb mixture firmly onto bottom of 8- or 9-inch square pan; set aside.
BEAT cream cheese and powdered sugar in large bowl with electric mixer on medium speed until light and fluffy. Add peanut butter; mix well. Gently stir in 2 cups of the whipped topping. Spread evenly over crust.
REFRIGERATE 4 hours or until firm. Top with the reserved crumb mixture and remaining whipped topping just before serving. Store leftover dessert in refrigerator.