Cook bacon in a 2- to 3-quart heavy saucepan over moderate heat, stirring, until golden, about 5 minutes.
Reduce heat to moderately low, then add onion, bell pepper, and celery. Cook, stirring until softened, about 5 minutes.
Stir in potato, bottled clam juice, and tomatoes (with juice) and simmer, covered, 10 minutes.
Stir in clams and simmer, covered, stirring occasionally, until clams open wide, 8 to 10 minutes. (Discard any clams that after 10 minutes have not opened as they are raancid.)
Remove pan from heat.
Remove most of clamshells with tongs, then detach clams and return them to chowder. (Keep a few in their shells for garnish.)
Stir in parsley and add salt and pepper to taste.