Preheat oven to 350 degrees F. Cook elbows according to package directions.
In a large nonstick skillet over medium heat, melt margarine. Blend in flour, salt, pepper and milk. Add cheese, stirring frequently until cheese is melted. Add cooked elbows to skillet with cheese mixture and stir to blend in completely.
Pour into a 13x9x2-inch casserole dish. Sprinkle bread crumbs over the top. Bake, uncovered for 15 to 20 minutes. Let stand about 10 minutes before serving.