BELGRADE, Yugoslavia -- Yugoslavia's two rebel republics, Croatia and Slovenia, declared independence last night in a move that would end the present Yugoslav state, arousing fears of civil war in the Balkan region.
The moves provoked a sharp reaction here in the Yugoslav capital. The federal Parliament issued a statement urging the army "to undertake measures to prevent the division of Yugoslavia and changes in its borders."
Sirens screamed and church bells boomed throughout Zagreb, the Croatian capital, as the speaker of the Croatian Parliament, Zarko Domljan, declared, "The State of Croatia is born."
A similar outpouring of emotion swept Ljubljana, the capital of neighboring Slovenia, after the Slovenian Parliament proclaimed the first independent, sovereign Slovenian state in history.
Both Slovenia and Croatia rejected an eleventh-hour appeal by the federal prime minister, Ante Markovic, himself a Croat, who warned of economic catastrophe if they moved toward independence. Mr. Markovic also asserted that he would use "all available means" at his disposal to prevent any unilateral dismemberment of the country. But after the independence declarations, he made no move to act on the Parliament's suggestions that the army ought to be used.
The two western republics also turned a deaf ear to last-minute attempts by the European Community and U.S. Secretary of State James A. Baker III to forestall the breakup of Yugoslavia. They said secession was the only option, since negotiations among the country's six republics over the past several months had led nowhere.
In proclaiming Croatia's independence, the republic's president, Franjo Tudjman, said the Croatian Parliament had fulfilled a "centuries-old dream" of the Croatian people and called on the international community to extend diplomatic recognition.
Slovenia's president, Milan Kucan, said that his republic wanted "an equal footing in relationships with groupings of nations such as the European Community or with other nations and states."
But while the two breakaway republics recognized each other immediately, they risk being ostracized in the international community. Most other countries -- including the United States and the European Economic Community's members -- are refusing to recognize their independence.
After trying unsuccessfully during a visit to Yugoslavia last week to keep Slovenia and Croatia from moving to independence, Mr. Baker warned of the danger that history -- in this case, the events that set off World War I -- could repeat itself.
His comments reflected what he had been told during a series of meetings with central government and republic leaders, an administration official said later aboard Mr. Baker's plane.
"If Yugoslavia splits up, with all of the problems in Kosovo and the Albanian diaspora and all the rest, you could see a triggering event here in the Balkans that could just repeat what we saw once before," the official said.
Serious doubts exist whether Slovenia and Croatia could survive economically. The rest of Yugoslavia is certain to cut off the market that they depend upon.
But the two republics see their defiance as the first positive step toward solving the future of Yugoslavia, a country of four official languages and at least 24 ethnic groups, coexisting in a historically fragile union since 1918.
Months of talks among the leaders of Yugoslavia's six republics have produced little but squabbling and recriminations. In effect, all the old Balkan divisions kept in check by communism and the late strongman Marshal Josip Broz Tito have been reawakened by the wave of democracy that has swept Eastern Europe.
And that -- rather than the federal government or army -- is what poses the biggest potential threat to the efforts of Slovenia and Croatia to go their own way. While the two republics have created their own armies, many different ethnic groups also have been building up their own militias and vigilante groups, and the recent bloodletting among them could become worse.
If Yugoslavia's federal army were to try to intervene, analysts here believe that civil war would almost certainly follow.
The army is troubled by its own ethnic divisions. Although 70 percent of the officers are Serbs, the army itself is ethnically mixed and may not respond to orders to put down ethnic trouble.
Even without federal army intervention, the potential for violence in Croatia exists between the Croats and more than 700,000 ethnic Serbs who live in enclaves in Croatia. These enclaves would like to declare their own independence and join with Yugoslavia's largest republic, Serbia. Serb-Croat violence in the enclaves has already claimed more than 20 lives in the past two months.
Both Slovenia and Croatia have created formidable private armies over recent months and said they would not hesitate to use them. Between them, they number 140,000 men -- just 40,000 fewer than the federal army itself.
And the armies are bristling with arrays of weaponry ranging from Singaporean machine guns to Soviet-made armed helicopters -- all obtained illegally during the past eight months.
Croatia's force, totaling about 70,000, even includes 5,000 Canadian Croats who have been training with it in response to a jTC call from Mr. Tudjman to help defend Croatia. "They'll make good killers," a senior official was quoted as telling a NATO ambassador here.
One U.S. official expressed the fear yesterday that if violence broke out in Yugoslavia, it could spread through a chain of interethnic rivalries. So far, this is no more than a nightmare scenario.
The United States hopes that after the declarations of sovereignty, the republics still will be able to negotiate with the central government and, as one official said, find a "basis for unity."