Meanwhile, melt margarine in large saucepan over medium heat. Add garlic; cook and stir 30 to 60 seconds. Stir in flour and pepper; cook and stir until mixture is bubbly. Gradually add milk, stirring constantly, until mixture boils and thickens. Remove from heat. Reserve 1 tablespoon each American and mozzarella cheese for top. Add remaining cheeses to sauce; stir until melted.