Microwave 2 Tbsp. margarine in large microwaveable bowl on HIGH 25 sec. or until melted. Stir in dry jelly powder. Microwave 15 sec.; mix well. Add 3 cups marshmallows; toss to evenly coat. Microwave 1-1/2 min. or until marshmallows are completely melted and mixture is well blended, stirring after 45 sec. (Caution: Bowl might be hot.) Add 3 cups cereal; mix well.