Cook garlic, onions, bay leaf, oregano, and red pepper flakes with salt and pepper in oil in an 8-quart heavy pot over moderate heat, stirring, until onions are softened, about 5 minutes. Stir in bell pepper and tomato paste and cook, stirring, 1 minute. Add wine and boil until reduced by about half, 5 to 6 minutes. Add tomatoes with their juice, clam juice, and broth and simmer, covered, 30 minutes. Season with salt and pepper.