Mitterrand, in Sarajevo, Pledges to Break Siege : Diplomacy: Tearful Bosnians cheer French leader’s visit. But their optimism about aid is muted.

French President Francois Mitterrand staged a daring visit to embattled Sarajevo on Sunday and vowed to break a Serbian blockade threatening the city’s 300,000 trapped citizens with starvation.

Hours later, Serbian forces relinquished control of Sarajevo’s shattered airport to United Nations peacekeepers so it can be reopened for humanitarian relief flights, the Tanjug news agency reported.

The first such flights, two French air force transport planes, each loaded with 6.5 tons of food and medicine, landed Sunday night in Split on Croatia’s Adriatic coast and planned to fly into the ravaged capital of Bosnia-Herzegovina this morning.

In Paris, the Defense Ministry announced that more such flights are being readied and will depart from France beginning today.

The apparent breakthrough generated only cautious optimism in beleaguered Sarajevo. U.N. officials said that formal reopening of the airport would take at least a week. Also, Serbian forces controlling access to the city were thought to have backed down more out of fear of foreign military intervention than out of concern for starving civilians, suggesting that the siege could be replayed as soon as Western mediators turn their attention elsewhere.

Nevertheless, hundreds of grateful Sarajevans braved a day out of their bunkers to thank Mitterrand for his initiative. Belgrade television showed tearful residents waving and blowing kisses from the debris-strewn sidewalks and chanting “Vive la France!”

Mitterrand, the first foreign leader to visit Bosnia since a Feb. 29 referendum endorsed independence and sparked Serbian rebellion, said that military force would be used if necessary to protect the relief flights and end the suffering brought on by the three-month siege that has killed thousands.

These developments in Bosnia unfolded as the U.N. Security Council prepared for a previously scheduled session this morning, apparently poised to act quickly to launch a massive airlift of food and supplies if the truce holds as hoped.

Diplomatic sources said that if all parties appear to be meeting U.N. demands for a cease-fire, the council probably will assign Canadian troops already in the region to take charge of airport security and clear the cluttered runways.

Today’s council session, set up late last week, initially had been slated to consider possible U.N. military intervention in Bosnia if the Serbs did not comply with a 48-hour truce deadline laid down Friday by U.N. Secretary General Boutros Boutros-Ghali.

Western sources said Sunday that in view of Mitterrand’s initiative, apparently undertaken without his informing U.N. and other Western officials in advance, it was unlikely that the council would consider a military operation, even if a truce is not fully in place by this morning. “They ought to have a little more time,” one diplomat said.

(President Bush initiated intensive phone consultations with allies over the weekend on ways to break the Bosnian blockade, the New York Times reported.)

A glaring illustration of the dangers and complexities of the Bosnian conflict was provided Sunday when the French president was forced to take cover for a time in an airport building when gunfire erupted as he was preparing to leave Sarajevo after his five-hour visit.

Earlier, one of two helicopters that brought Mitterrand and his party to Sarajevo from Split, where they had spent Saturday night, was damaged by gunfire from the ground and was judged unfit for the return trip. Then the presidential Falcon fanjet, brought from Split to Sarajevo for the party’s return trip, suffered minor damage to a wing when it was accidentally rammed by a vehicle.

“We’ve had a catastrophic toll,” Mitterrand joked to French reporters on the scene. “We only have one helicopter to get us back to Paris.”

In another sign of the troubled times gripping the Balkans, Serbia’s Crown Prince Alexander wore a flak jacket under his double-breasted suit while addressing a Belgrade demonstration against Serbian President Slobodan Milosevic.

“I am with you!” the pretender to the vacant Serbian throne told 100,000 protesters outside the Yugoslav Parliament.

It was the largest action against Milosevic since he came to power four years ago. The gathering drawing prominent religious, political and cultural figures coincided with Serbia’s most important national day, Vidovdan or St. Vitus Day. On June 28, 1389, Serbs were defeated by Ottoman Turkey in the bloody Battle of Kosovo and lost their independence for the next 500 years.

Vidovdan has even more ominous resonance for Serbs in Sarajevo, because it was on that date in 1914 that a Serbian nationalist assassinated Austrian Archduke Franz Ferdinand, setting off World War I.

Although opposition to Milosevic has been growing due to harsh U.N. sanctions imposed on Serbia for provoking the Bosnian conflict, Sunday’s demonstration lacked the intensity of a brewing revolution and organizers continued to advise restraint to prevent Serb-versus-Serb bloodshed.

The crowd--many sporting nationalist garb suggesting they support Serbian rebellion in Bosnia--repeatedly chanted for restoration of the monarchy and for Milosevic to resign.

However, the Serbian strongman accused of whipping up long-dormant ethnic tensions throughout the Balkans has given no indication he will relinquish power peacefully.

Police were out in force with water cannon at the ready, but there were no violent incidents reported during the daylong gathering that filled streets and parks for several blocks.

A similar protest against Milosevic was staged May 31, a day after the United Nations imposed an oil and trade embargo against Serbia and its close ally, Montenegro, for arming Serbian rebels engaged in a deadly land grab.

More than two-thirds of Bosnian territory is now in the hands of Serbian guerrillas, who have expelled Muslims and Croats to swell the Yugoslav refugee wave to at least 2 million. Bosnian officials last week reported 7,440 confirmed deaths and 35,000 missing, many of whom are presumed dead.

Serbian opposition leader Vuk Draskovic said that Milosevic has caused Serbia to be “evicted from the civilized world” and accused him of involving Bosnian Serbs in a violent campaign he now wants to abandon.

Mitterrand, who visited a city deemed too dangerous for foreign mediators and armed U.N. peacekeepers, toured the artillery-pounded ruins of Sarajevo’s historic center in the company of Bosnian President Alija Izetbegovic.

“I did not come to Sarajevo to negotiate with anyone. I came to answer for myself what is happening in Sarajevo,” Mitterrand told news agency reporters during his visit.

“We are going to send humanitarian aid to Sarajevo, and, if necessary, we’ll use force to protect it,” the Associated Press quoted Mitterrand as saying.

After meetings with U.N., Muslim and Bosnian leaders, Mitterrand visited a military hospital, where Belgrade television showed the beleaguered staff applauding his arrival and shedding tears.

The 75-year-old president also laid flowers at the Vase Miskina street site where at least 20 people died a month ago when a grenade fired from Serbian positions struck a crowd of shoppers lined up to buy bread.

Mitterrand’s dramatic mission was not announced until he was airborne from Lisbon, where he and other European Community leaders met for a weekend summit. The gathering endorsed the use of military force to free Sarajevo airport, if needed, but failed to generate any specific proposals for lifting the siege.

EC and U.N. efforts to intervene in the Yugoslav crisis that turned violent more than a year ago have been hampered by bureaucracy, indecision and frequent delay.

Mitterrand’s visit was greeted with general enthusiasm and praise in France, even from members of the political opposition.

A typical reaction came from Nicolas Sankozy, a leader in the Gaullist Rally for the Republic Party who praised Mitterrand for his “panache” and humanitarian “beau geste.” Another Gaullist figure, Michel Barnier, said: “We needed this symbolic gesture.”

Times staff writers Art Pine in Washington and Rone Tempest in Paris contributed to this report.