Man in Middle of AOL Deal Is Now at Center of a Storm
Stephen M Case, architect of America Online and Time Warner merger, becomes target of growing criticism by analysts and investors after chairman Robert W Pittman resigns; Securities and Exchange Commission has opened probe into accounting practices at AOL that may have inflated past revenue; some analysts say Case's role as merger's architect makes him liability as AOL Time Warner tries to rebuild its credibility; company's directors, with Pittman's departure from board, are now evenly divided between Time Warner and AOL members; photo (M)