Spread rice in the bottom of a 9x13 inch baking dish; set aside.
In a medium saucepan melt butter or margarine and stir in flour until smooth. Gradually add milk, bouillon granules, seasoned salt, garlic powder and pepper. Stir all together and bring to a boil. Let simmer and stir for 2 minutes or until thickened and bubbly. Reduce heat; add chicken, cheese and sour cream. Stir until cheese is melted. Mix all together and pour mixture over rice.
Melt 1/2 cup butter or margarine in saucepan and toss with crushed cracker crumbs. Sprinkle crumb mixture over casserole. Bake in the preheated oven for 10 to 15 minutes or unti heated through.