ALMOST FIVE YEARS after German unification, writers in the western and eastern halves of the country are still divided over whether they, too, should unite. The German PEN Center (East) - known as Ost-PEN - has come out strongly in favor of a merger with its West German counterpart, arguing that only one PEN center is now needed in the country. But its hopes of union in the near future were dashed at West-PEN's annual conference in May. Despite deep internal divisions, the delegates adopted a resolution stating that no merger could take place until Ost-PEN had given a full account of its members' involvement with the communist regime. They decided that the issue should be shelved for two years, allowing more time to be spent discussing literature and what some members described as the worthier causes that the PEN centers serve.