Remove giblets from squabs; reserve for other uses. Rinse squabs with cold water; pat dry.
Combine butter, onion, celery, and green pepper in a large skillet; sauté until vegetables are tender, and set aside.
Place chicken broth in a medium saucepan; bring to a boil. Stir in rice. Reduce heat; cover, and simmer 20 minutes or until rice is tender and broth is absorbed. Remove from heat. Add sautéed vegetables to the rice; stir well. Stir in remaining ingredients.
Stuff squabs with rice mixture (about 2/3 cup per squab). Place remaining rice mixture in a lightly greased 13- x 9- x 2- inch baking dish. Arrange stuffed squabs on top of rice mixture. Bake at 400° for 45 minutes.