Montenegro, the only Balkan republic that remains linked with Serbia after the collapse of the former Yugoslavia, is planning to hold a vote in mid-May that could lead to it becoming an independent state.

How the referendum is conducted is widely seen as critical to the stability of the region, with Western officials fearing that a disputed outcome could lead to unrest, or a possible split down the center of the mountainous republic.

Solana and his envoy to the region, Miroslav Lajcak of Slovakia, have urged Montenegro’s pro-independence government and its opposition, which wants to remain in union with Serbia, to agree to clear rules ahead of the vote.

They have suggested that Montenegro be allowed to secede from the two-state federation if 50 percent of the electorate takes part in the vote and 55 percent of voters opt for independence.

On Saturday, Montenegro’s opposition parties agreed to back the EU proposals. A meeting of European foreign ministers in Brussels is expected to unanimously endorse the recommendations on Monday. However, the Montenegrin government has indicated it is opposed to the guidelines. In a statement released Sunday, Solana’s office urged the Montenegrin government to follow the opposition’s example.

"A similar decision by the government coalition would allow the referendum process to begin immediately, under the best auspices and with the full backing of the European Union," said Christina Gallach, Solana’s spokeswoman.

With opinion polls indicating voters in favor of separation from Serbia by a narrow margin, the government is concerned that the EU guidelines would give the pro-Serbia minority an unfair hold over the republic.

"The decision belongs to the majority and not the minority," the prime minister of Montenegro, Milo Djukanovic, said on Thursday. "The EU’s formula contains a virus which is dangerous to the stability of society when it comes to the implementation of the results," he added, according to the region’s news agencies.

The government has proposed that referendum should be valid if 41 percent of the electorate votes. The Montenegrin Parliament is expected to give its formal response to the European Union’s proposal on Wednesday.

Montenegro was internationally recognized as an independent state in 1878 but was absorbed into Yugoslavia at the end of World War I. Throughout the 1990s, the country set itself apart from Serbia’s authoritarian rule under the Yugoslav president, Slobodan Milosevic.

However, after the removal of Milosevic from government in elections in 2000, Djukanovic lost some Western support, notably over his failure to crack down on organized crime, like the trafficking of cigarettes and people across the Adriatic sea to Italy. This reputation, and fear that an independent Montenegro could add grist to separatist desires in the United Nations-administered province of Kosovo, and Bosnia’s Serb republic, dulled the international community’s support for the state breaking away from Yugoslavia.

It was Solana himself who brokered an agreement in 2003 over a new Constitution for Serbia and Montenegro, bringing a formal end to the Yugoslav federation. That agreement provided for the possibility of a referendum on Montenegro’s status this year.

Since 2003, Djukanovic’s party and his coalition partners have sought to cement Montenegro’s move toward independence. The republic, which has a population of just over 600,000, already has a separate customs service, uses a separate currency – the euro – and in the last three years has adopted a new flag and national anthem, and introduced a national day.

Unlike Bosnia, Croatia and Kosovo – former Yugoslav regions that all saw ethnic conflict during the 1990s – Montenegro remained largely peaceful, and political and ethnic divisions are more ambiguous. The majority of Montenegrins are Orthodox Christians and speak Serbo-Croat.

However, the political divide over the republic’s future has clear geographic boundaries. The northeast of the country, with the exception of the Slavic Muslim dominated region of the Sandjak, favors union with Serbia. The southwest favors independence.

In the event of a disputed outcome to the referendum, diplomats in Belgrade say, those divisions would be worrying.