Place potatoes in a large saucepan; add water to cover. Bring to a boil. Reduce heat; cook, uncovered, 7-9 minutes or until tender. Drain, reserving 1/2 cup potato water.
Meanwhile, in another large saucepan, heat butter over medium heat. Add celery, carrots and onion; cook and stir 6-8 minutes or until tender.
Stir in flour until blended; gradually stir in cream and reserved potato water. Bring to a boil; cook 2-3 minutes or until slightly thickened, stirring occasionally. Add clams, seasonings and potatoes; heat through.