In a kettle saute the onion, the garlic, the celery, and the bell pepper in the oil over moderately high heat, stirring, until the vegetables are softened, add the tomatoes, the clam juice, the lemon juice, the marjoram, the bay leaf, and the pepper, and simmer the mixture, covered, for 30 minutes. Stir in the halibut and the potatoes, peeled and cut into 1-inch pieces, and simmer the mixture, covered, for 30 minutes, or until the potatoes are cooked through. On a clean work surface knead together the butter and the flour until the mixture forms a paste. Stir the paste into the halibut mixture, a little at a time, and simmer the stew over moderate heat until it is thickened. Remove the bay leaf and garnish the stew with the parsley. Serves 4 to 6. fish 32