McCain, Sure on Military Issues, Is Less Certain on Domestic Ones
Sen John McCain can speak in great detail about military issues, but he seems less fluent on domestic matters; his pledge that he will never be guided by opinion polls but will always act 'on principle' applies only to national security matters; McCain says that on domestic affairs, it will be helpful to use polls to find out what Americans want; McCain's ideas on domestic matters seem far from fixed or fully developed despite his conservative voting record in 17 years in Congress and his image as reformer; he has yet to explain fully how his vision of conservative reform will translate into comprehensive domestic agenda; photo (M)