HEAT oven to 350°F.
COOK pasta as directed on package, omitting salt.
MEANWHILE, combine cheeses; set aside. Melt 2 Tbsp. butter in large saucepan on low heat. Add peppers and garlic; cook 30 sec. Add flour; cook and stir 2 min. or until hot and bubbly. Gradually stir in milk. Bring to boil on medium heat, stirring constantly; simmer on low heat 3 to 5 min. or until thickened, stirring constantly. Remove from heat. Add 1-1/2 cups cheese mixture; stir until melted.
DRAIN pasta. Add to cheese sauce; mix well. Spoon into 1-1/2-qt. casserole sprayed with cooking spray; top with remaining cheese mixture. Melt remaining butter in small skillet on medium heat. Add bread crumbs; cook and stir 1 to 2 min. or until lightly toasted. Sprinkle over cheese mixture.
BAKE 20 min. or until heated through.