Rinse chicken under cold running water. Place chicken in 8 to 10 quart stockpot. Add 3 quarts water.
Cut leeks crosswise into 1/2 inch slices, including 23 inches of green tops. Add to pot with onion, carrots, barley, salt, white pepper and herbs, tied in cheesecloth bag. Bring to boil over high heat. Reduce heat to low. Simmer, partially covered, until chicken is very tender, about 3 hours. Skim off and discard foam that appears on top during cooking.
When chicken is cooked, place it on large platter. Let stand until cool enough to handle. Remove skin and pull meat off bones. Discard skin and bones. Cut meat into bite-sized pieces. Return to pot. Simmer 5 minutes longer. Skim off fat from top. Discard herb bag. Serve soup hot, sprinkled with parsley. 10 to 12 servings.