MELT margarine in large skillet on high heat. Add steaks; cook 5 min. on each side or until cooked through. Remove from skillet; cover to keep warm.
ADD mushrooms and onion to skillet; cook and stir until tender. Stir in flour until well blended.
STIR in milk gradually. Bring to boil, stirring constantly. Stir in steak sauce; spoon over steaks. Serve with the rice.