The transition to the euro as the official currency of 12 European Union countries Jan. 1 is expected to have its problems, but perhaps nowhere more so than in France, where as many as 400,000 bank employees are poised to strike Jan. 2. Such action would close down most banks at a time when the French will need to be converting their francs and could produce several days of financial chaos. The strikes are being called to force officials to provide additional training and compensation for the task of working through the transition.