Stir together first 4 ingredients with a fork until crumbly. Press into a lightly greased 13- x 9-inch pan.
Bake at 375° for 15 minutes. Cool in pan on a wire rack.
Beat whipped topping, cream cheese, and powdered sugar at medium speed with an electric mixer until smooth. Spoon over prepared crust. Cover and chill.
Stir together sugar and cornstarch in a saucepan; whisk in 1 cup water until smooth. Stir in blueberries, and bring to a boil. Boil, stirring constantly, 2 minutes. Remove from heat; cool. Pour over cream cheese mixture. Cover and chill at least 2 hours.