The old crusaders are getting just a little creaky: Dr. Arnold S. Relman, 88, has a hearing aid and the hint of a tremor; Dr. Marcia Angell, 72, osteoporosis and arthritic hands. Their joint crusade, stated repeatedly in editorials for The New England Journal of Medicine and since expanded in books and dozens of articles, is against for-profit medicine, especially its ancillary profit centers of commercial insurance and drug manufacture. Some have dismissed the pair as medical Don Quixotes, comically deluded figures tilting at benign features of the landscape. Others consider them first responders in what has become a battle for the soul of American medicine.