Cook pasta according to package directions; drain well. Melt 6 Tbs. butter in saucepan. Add flour and seasonings; blend. Stir in milk gradually. Cook over low heat, stirring constantly until thickened. Add 1 cup cheese; stir until melted. Stir in cooked spaghetti and tuna. Pour into a 1 1/2 quart greased baking dish. Melt remaining 2 Tbs. butter; add bread crumbs and remaining cheese; toss lightly. Pour over surface. Bake in a moderate oven (375º F.) 30-35 minutes or until golden brown. Makes 6 servings.