PREHEAT oven to 350°F. Grease two (8- or 9-inch) round cake pans; set aside. Prepare cake batter as directed on package. Pour half of the batter into medium bowl. Add dry jelly powder; stir until well blended. Spoon half of the white batter and half of the pink batter, side by side, into each prepared pan.
SWIRL batters together using a teaspoon. (Do not overswirl, or the colour of the cake will be all pink and not pink and white marbled.) Bake 30 min. Cool 30 min. in pans. Remove to wire racks; cool completely.
MIX sour cream and icing sugar in medium bowl until well blended. Gently stir in whipped topping. Place one of the cake layers on serving plate; spread top with 1 cup of the whipped topping mixture. Top with 1 cup of the strawberries. Top with remaining cake layer. Spread top and side of cake with remaining whipped topping mixture. Top with remaining 1/2 cup strawberries just before serving. Store leftover cake in refrigerator.