The United States has begun a painful reassessment of the alignment of social responsibilities among levels of government and between the public and private sectors. As this struggle unfolds, pressures on the government are intensifying to check the steady increase in the portion of the federal budget that serves the elderly, including the funds that finance Medicare. This exercise will be given to many fits and starts, particularly during election years, but it will very probably have important short-term and long-range consequences for Medicare.This fledgling movement, which stems from President Reagan's goal to retrench the scope of government and . . .