Place alternate layers of chicken and oysters in bottom of greased 2 qt. casserole.
Blend together flour and ½ c. chicken broth (or cold water). Add to remaining 2 c. chicken broth. Add celery, onion, salt, pepper and peas and carrots. Cook over medium heat, stirring constantly, until mixture comes to a boil. Simmer 5 minutes. Pour over chicken and oysters.