Preheat oven to 350F (325F for glass dish). Place margarine in a 9x13 pan and melt in preheating oven. Sprinkle crumbs evenly over melted margarine. Next, pour the sweetened condensed milk over the crumbs. Top with chocolate and peanut butter chips; press down firmly.
Bake 25-30min. until lightly browned. Be careful not to leave bars in oven too long; they are difficult to get out. Cool and cut into bars. Store loosely covered at room temp.