BERLIN, Nov 1 (Reuters) - Serbia must decide whether it wants to join the European Union or enter into a partnership with Russia, Germany told Belgrade on Tuesday, two days before six Western Balkan countries are scheduled to discuss closer cooperation in Berlin.Serbia, which was bombed by NATO two decades ago but now seeks to join the European Union, has long struggled to balance historically close ties with Russia against aspirations for economic and political integration with the West.An agreement between Serbia and Russia on enhanced cooperation had been met with surprise and disappointment, and was a poor fit with expectations that EU accession candidates should also adopt EU sanctions against Russia, the representative said.Serbia, an accession candidate since 2012, decided in September to hold regular foreign policy consultations on bilateral and multilateral activities with Russia.One got the impression that Serbian President Aleksandar Vucic was well aware of his pendulum position, the German government representative said."