PREHEAT oven to 350°F. Mix graham crumbs, margarine and sugar. Reserve 1-1/2 cups of the crumb mixture; press remaining crumb mixture firmly onto bottom of 13x9-inch baking pan.
BAKE 10 minutes. Remove from oven; cool completely.
SPREAD half of the ice cream over crust. Sprinkle with 1 cup of the reserved crumbs; press lightly into ice cream. Top with remaining ice cream; cover with whipped topping. Sprinkle with remaining 1/2 cup crumbs. Freeze 4 to 6 hours or overnight until firm. Cut into 24 squares to serve. Store leftover squares in freezer.