Slice 1 cup of strawberries and halve remaining 3 cups.

Pour gelatin into a heat-proof bowl and add boiling water. Stir until completely dissolved, at least 2 minutes. Pour cold water into a 2-cup measure and add enough ice cubes to bring level to 2 cups. Add cold water and ice to gelatin and stir until melted. Refrigerate until slightly thickened to the consistency of unbeaten egg whites, about 5 minutes.

Meanwhile, line a 13x9-inch baking dish with sliced pound cake.

Remove gelatin from the refrigerator and stir in sliced strawberries and 1 cup blueberries. Spoon mixture over cake slices in the baking dish. Refrigerate until firm, about 4 hours.

Beat cream cheese and sugar together in a bowl until smooth. Stir in whipped topping and spread mixture over gelatin in the baking dish. Arrange sliced strawberries and remaining blueberries to create an American flag.