BELGRADE, June 7 (Reuters) - Serbian President Boris Tadic urged Serbia and Montenegro on Wednesday to avoid another "sad and messy" separation in the Balkans following Montenegro's declaration of independence at the weekend.
Serbs should "show how, in this separation, we can maintain the historical good relations between us".
"Too many of our citizens will live in each other's state to allow pettiness to prevail," Tadic wrote in an op-ed piece in the Washington Post.
His political rival, Prime Minister Vojislav Kostunica, has not congratulated Montenegro on its May 21 referendum vote to end the union with Serbia, dissolving a partnership going back to 1918. His acceptance of it has sounded grudging.
Kostunica says there can be no "velvet divorce" with Montenegro, as with Czechoslovakia in January 1993, and last week he turned down an offer of European Union help in smoothing the separation.
In language clearly aimed at his own electorate as much as international observers of ex-Yugoslavia's slow transformation, Tadic said it was high time for Serbia, now a sovereign state, to focus on real challenges such as raising living standards.
Some diplomats speak of a sense of political drift in Serbia, its hopes of quick progress on the road to EU membership dented by Brussels' decision to freeze talks because Belgrade has not delivered war crimes fugitive Ratko Mladic.
Political analysts expect a snap election later this year in which Tadic's Democratic Party can aim to unseat Kostunica's fragile minority coalition, which is already on the ropes.
"This is a strategically vital year for Serbia," the president wrote, in a reference to talks on whether the 90 percent ethnic Albanian majority in Kosovo province -- run by the United Nations and NATO -- will get the independence from Belgrade they demand or remain part of Serbia.
"We hope that responsible leadership from Serbia will be reciprocated by (the European Union and NATO). But Serbs in Kosovo would need "exceptional provisions for their protection" if a mass exodus is to be avoided, he said.
The U.N. has contingency plans for 50,000 Serbs leaving Kosovo if it gets independence -- a probability in international eyes but a prospect Kostunica refuses to countenance.
"Our political leadership faces choices of a kind that have rarely confronted a country that is both democratic and at peace," Tadic said.
Those who are hiding Mladic are "the least patriotic of Serbs. They are part of that political culture that hijacked Serbia and its history some 15 years ago".
He urged the forces that brought democracy to Serbia in October 2000 by toppling strongman Slobodan Milosevic to "rise to the challenge posed by the immediate future, uniting to complete unfinished business they embarked five years ago"