Yugoslavia Leadership Falls Apart : Ethnic strife: A virtual coup by Serbs leaves the nation without a president. Croatians delay any move to secede. New violence is feared.

The Yugoslav leadership collapsed Friday after what amounted to a Serbian-led coup d’etat , leaving the crisis-torn country without a president or a forum to negotiate escape from a looming civil war.

The power vacuum left open the possibility of a military takeover, moves by Croatia and Slovenia to secede, and uncontrollable outbreaks of violence between armed Serbs and Croats.

Croatian President Franjo Tudjman huddled with advisers through the night to ponder his next move after his republic was forced out of the federal presidency--the last significant Yugoslav institution except for the army--in a humiliating showdown with rival Serbia.

Croatian authorities have threatened to convene an emergency session of the republic’s Parliament in Zagreb to begin pulling out of Yugoslavia in protest over Croatia’s being denied its constitutionally mandated term as federal president.

But republic leaders put off any precipitous moves, saying they would wait at least until early today to see if Serbia ceases its attempt to undermine federal authority.

“Serbia and its supporters will show the world whether they are willing and able to follow the constitution, or whether they have abandoned it completely,” said Zvonko Lerotic, one of Tudjman’s chief aides.

If it is deprived of its role in the federal leadership, Croatia will negotiate with the other non-Communist republics to form a new alliance of sovereign states, Lerotic said, adding that “for all practical purposes, two Yugoslavias have existed for a long time.”

Federal Prime Minister Ante Markovic said his government had formed an emergency council to act in the absence of the collective presidency. But Markovic and his Cabinet have virtually no support from the battling republics and are likely to be ignored in their attempts to take charge of the foundering federation.

Control of the presidency was to have passed from Serbia to Croatia on Wednesday, according to an intricate power-sharing system designed by the late Yugoslav leader Josip Broz Tito.

All eight presidential members--one from each of the six republics and two Serbian-controlled provinces--gathered twice in an attempt to inaugurate Croatia’s Stipe Mesic as head of state and commander of the armed forces.

At the first session Wednesday, Serbia rallied its two subjugated provinces to vote against Mesic, and the delegate from Montenegro abstained, leaving what should have been a routine endorsement one vote short of the five needed for approval.

The interim delegate from Montenegro, a republic predominantly populated by Serbs, refused to cast a vote because the permanent presidential representative had not yet been confirmed by the Yugoslav Parliament. That technical delay--believed to have been instigated by Serbia--was cleared when a special parliamentary session was called Thursday and the Montenegrin and two other new appointees were sworn in.

A second session of the presidency was convened Friday, presumably after Croatia had been promised that the Serbian blockade would be ended.

When the stalemate continued into the night, Mesic and the presidential delegates from Slovenia and Macedonia walked out, declaring the ruling body in violation of its own laws.

“Croatia will no longer accept the presidency’s decisions as legitimate,” Mesic told Zagreb Radio after storming out of the session. “Croatia will call its Parliament into emergency session because it can no longer bear this insult.”

Mesic said he considers himself Yugoslavia’s president, despite the Serbian-led boycott of his leadership. But his immediate return to the Croatian capital of Zagreb and warnings that the republic would proceed with plans to declare full independence suggested that he had given up on attempts to negotiate with the Serbian-led faction of the presidency.

Slovenia has also threatened to step up its secession, already set for June 26.

“Yugoslavia is no more,” Slovenian President Milan Kucan stated after the first rebuff of Mesic. “This is Serbia against all the other republics. Well, Slovenia did not join Yugoslavia to serve Serbia.”

By preventing Mesic from assuming his duties, Serbia, a republic of 9 million, flaunted the disproportionate power it enjoys in the federation of 24 million.

With four of the eight votes locked up, Serbia can block any decision by the federal presidency, which must approve directives with a majority of at least five.

That makes it unlikely that Mesic could wield much influence over the troubled federation, even if allowed to take office. And the Serbian-commanded armed forces have already been used to the largest republic’s advantage in the volatile face-off between Serbian militants and Croatian police.

Mesic, a 56-year-old lawyer and former political prisoner, would have been Yugoslavia’s first non-Communist president. What was more unpalatable to his Serbian counterparts was Croatia’s apparent determination to disengage itself from the federation.

Since electing a non-Communist, nationalist government last April, Croatia has declared its intention to secede and form an independent state unless a looser and more equitable arrangement among the republics can be negotiated. It has been joined in that effort by Slovenia, Macedonia and Bosnia-Hercegovina.

Serbia’s hard-line Communist president, Slobodan Milosevic, refused to discuss any realignment of the republics, instead declaring that all Serbs must continue to live in a single state.

With 2 million Serbs living outside Serbia’s borders, Milosevic’s claim has been seen as a threat to incorporate Serbian-populated areas of Croatia into an expanded Serbian republic.

About 600,000 ethnic Serbs are among Croatia’s 5 million citizens.

The conflict has systematically escalated into recurring ethnic violence, which has already killed at least 19 this month.

Federal army troops have been deployed to keep the peace between armed Serbs and Croatian police officers seeking to regain control of police stations and city halls in predominantly Serbian regions such as Knin, in southern Croatia, and Slavonia in the far northeast of the republic.

While fewer instances of ethnic bloodletting have occurred since the military deployments, Croatia accuses the army of setting up a protective cordon around the illegally armed Serbs in preparation for a Serbian takeover of those territories.

The political brinkmanship orchestrated by Serbia amounted to a de facto coup, as it has stripped Yugoslavia of its last surviving leadership body.

The federal Communist Party fell apart two years ago, the Parliament is an unrecognized holdover from the one-party system and the Markovic government has been blamed for the severe economic crisis that has resulted from each republic acting in its own interest instead of that of the federation. The government is virtually bankrupt, and a no-confidence vote against Markovic has been called for next Thursday.

The presidency played a key role in recent crisis talks aimed at salvaging a political alliance of the republics now torn by differences over ideology, religion, language, culture and history. Without it, there remains no forum for addressing the colossal economic and security problems confronting the country.

Yugoslavia was formed in 1918 from warring states long controlled by Ottoman Turkey and Austria-Hungary. But few expect the federation to hold together through this year.

The increasingly likely breakup has worried many Europeans, especially those whose countries share a border with Yugoslavia and would be most likely to incur waves of refugees from chaos and violence.

While the bloodshed so far has mostly involved Serbs and Croats, there is a risk that neighboring powers such as Greece, Hungary and Albania could be drawn into the conflict if there is a threat to the safety of those sizable ethnic groups in Yugoslavia’s border regions.

The atmosphere is especially tense in the Serbian province of Kosovo, where ethnic Albanians who make up 90% of the population there have been under virtual martial law by Serbian forces for two years.

U.S. officials have spent the week nervously watching the developing crisis, worried about the impact that ethnic unrest in Yugoslavia could have elsewhere in Eastern Europe but aware that there is little, if anything, that the United States and its allies can do about it.

With little else to do, Bush Administration officials have tried applying verbal pressure on Serbia’s Communist government to abandon its current course.

“We attach great importance to the orderly transfer of constitutional authority,” State Department spokesman Richard Boucher said Friday. “We are disappointed that Serbia continues to block such a transfer despite assurances to the contrary.”

Officially, the Administration still favors “a united and democratic Yugoslavia,” a solution that few still consider possible. President Bush’s aides say the Administration is clearly opposed to any resolution of the crisis that would allow Serbia to dominate the democratically elected, non-Communist governments of Slovenia and Croatia.

At the same time, the Administration is uncomfortable with the idea of a final breakup of the Yugoslav confederation, fearing that it would set a dangerous precedent for ethnic unrest in other countries such as Czechoslovakia and, ultimately, the Soviet Union.

Times staff writer David Lauter in Washington and special correspondent Michael Montgomery contributed to this article.