In a 4-quart Dutch oven cook bacon until crisp. Remove bacon, reserving 1 tablespoon drippings in the pan. Drain bacon on paper towels; crumble and set aside.
Add carrots, parsnips, and onions to Dutch oven. Cook over medium heat for 8 to 10 minutes or until brown, stirring occasionally.
Add potatoes, chicken broth, garlic salt, and pepper. Bring to boiling; reduce heat. Cover and simmer about 15 minutes or until potatoes are tender. (At this point the soup can be cooled, covered, and chilled in the refrigerator overnight.)
In a small mixing bowl stir together melted margarine or butter and flour. Stir flour-margarine mixture, milk, and corn into chowder mixture in Dutch oven.
Cook and stir over medium heat until slightly thickened. If desired, add oysters and liquid to soup; heat through. Sprinkle each serving with crumbled bacon and chives or parsley, if desired. Makes 12 cups (8 to 10 side-dish servings).