Heat margarine in a large saucepan and cook onion, celery and carrots over low heat until tender, stirring occasionally. Add flour and cook for 5 minutes, stirring constantly. Do not brown. Gradually stir in chicken broth until blended. Bring to a boil, cover, and cook over low heat 5 minutes. Add green and red pepper, rice and chicken and heat another 5 minutes. Stir in hot half and half. Heat but do not boil. Season to taste with salt and pepper. Makes 10 cups. * This soup may be made ahead and frozen