It was supposed to be the day the European Community brought peace to Osijek.
But Serbian guerrillas fired 120-millimeter mortars into the city's square, killing a woman and wounding other people. Then a Yugoslav officer arriving to represent the army in cease-fire arbitration was nearly lynched by an angry local crowd. Finally, Croatian militiamen fired artillery back at the Serbs.
Eight days after a cease-fire brokered by the European Community was signed to put an end to the two-month war between the militias of the separatist government of Croatia and the unionist insurgents from the republic's Serbian minority backed by the national army of the Yugoslav federation, the execution of a secure, monitored truce is proceeding fitfully.
European cease-fire monitors -- diplomats and military men known to the locals as "the ice cream men" for their white jumpsuits -- are taking up positions in the worst-embattled areas of Croatia.
To pave the way for these observers, a European envoy has been traveling by helicopter to the hot spots, seeking to get representatives of the army, the Croatian militia, and the Serbian rebels to put their signatures to a local cease-fire accord.
By Monday the envoy, Henry Wijnaendts, had obtained signatures on three such accords, two for Slavonia in eastern Croatia, a region that includes Osijek, and the third around Gospic, near the Adriatic. Today, he traveled to Knin, a Serb stronghold in southern Croatia, to seek a fourth.
Explaining his task to reporters on Monday, Mr. Wijnaendts said: "We make all the parties concerned sign these three points, that if somebody starts firing, the parties agree to discuss it, and not take the automatic reflex of shooting, and that they appoint liaison officers with one another, so that there is a man with the Croatian national guard and with the Serbs, and vice versa."
On Monday, the European Community sent five observers into Osijek, satisfied that the signing of the local truce assured their safe deployment.
"You should see this mission, my mission, as making it possible for the monitors to go in," said Mr. Wijnaendts, who is the Dutch Ambassador in Paris. "The monitors can only go in if there are reasonable assurances for their safety."
But today's shelling of Osijek, a city of 158,000 that has echoed for weeks to the sound of artillery in the suburbs, provides evidence of the difficulties that lie ahead. Serbian representatives signed the local cease-fire on Sunday, so nobody could say why at 5 A.M. they began firing mortar shells over the Drava River from the Serbian-controlled village of Bilje into Osijek's central Starcevic Square.
Observers from Denmark and the Netherlands, with Italian drivers, raced to a nearby army base, then jointly inspected the damage with Croatian city officials.
In the meantime, the army command in Zagreb dispatched a lieutenant colonel as a liaison officer. But when he stepped out of his limousine onto the square this afternoon, an angry crowd was drawn by the hated khaki uniform with the red star of the Yugoslav Army on the cap.
"He came here to see what his army did," said Bozidar Riba, a 65-year-old retired construction worker.
