Drain asparagus spears, reserving 1/2 cup of the liquid. Heat margarine in a saucepan. Add flour; blend. Gradually pour in asparagus liquid and milk. Stir constantly over low heat until sauce thickens and bubbles. Add cooked ham and seasonings. Gently stir in asparagus spears; heat through but do NOT boil. Serve in preheated serving dish.