NEW YORK (AP) - Kosmas Spiridellis, the top technology manager at the securities firm CIBC World Markets, may be precisely the sort of well-informed American who gives Y2K planners insomnia. Spiridellis is the main fixer of millennium bugs for his company, but he still plans to withdraw a few thousand dollars in cash, just in case there are glitches that cause bank computers to misread Jan. 1, 2000 as 1900. "We all have to be prudent," he maintains. Not so fast, many government and business leaders say. Such last-minute moves repeated the world over could create bigger problems than computer bugs themselves.