Arrange asparagus in a lightly greased 13- x 9-inch baking dish.
Melt 3 tablespoons butter in a heavy saucepan over medium heat; whisk in flour until smooth. Cook, whisking constantly, 1 minute. Gradually add milk; cook, whisking constantly, until thickened and bubbly. Stir in 1/2 cup cheese and salt, and pour over asparagus.
Stir together remaining 1/4 cup cheese, breadcrumbs, 1 tablespoon melted butter, and paprika; sprinkle evenly over casserole.
Bake at 350° for 25 to 30 minutes or until thoroughly heated.
*3 pounds fresh asparagus may be substituted. Snap off tough ends; remove scales with a vegetable peeler, if desired. Cook in boiling water to cover 3 minutes, drain.