In a large bowl, combine flour, 1/4 cup confectioners' sugar, pecans and margarine. Press into bottom of 13x9x2-inch baking pan. Bake 20 minutes. Set aside to cool.
In a mxing bowl, mix cream cheese and remaining 2/3 cup confectioners' sugar until creamy. Fold in 3/4 cup whipped topping. Spread cream cheese mixture over cooled crust.
In a mixing bowl, beat sweet potatoes, sugar and cinnamon until smooth. Spread over cream cheese mixture. Top with remaining whipped topping. Refrigerate.