Heat oven to 375*F.Combine blueberries, blackberries, lemon juice, 6 tablespoons granulated sugar and 2 tablespoons flour in a large bowl; transfer to 2-quart shallow baking dish.
Combine remaining flour and granulated sugar, brown sugar and cinnamon in medium bowl.With pastry blender, cut in butter until crumbly.Stir in walnuts.Sprinkle evenly over fruit.
Bake 40 to 45 minutes, until top is brown and fruit is bubbly.Cool on wire.Serve warm or at room temperature with vanilla ice cream or Cool Whip.
