BLEND cookie crumbs and margarine in small bowl. Press firmly onto bottom of 8-inch square pan; refrigerate until ready to use.
BEAT cream cheese and sugar in large bowl with electric mixer on high speed until light and fluffy. Add peanut butter and milk; beat until well blended. Stir in whipped topping.
SPREAD evenly over crust. Refrigerate 5 hours. Cut into 9 squares to serve. Store leftover dessert squares in refrigerator.