Yugoslav Fighting Growing Fiercer : Independence: The army sweeps into breakaway Croatia. Federal presidency’s chairman calls on soldiers to stop following their commanders’ ‘illegal’ orders.

The fighting in Yugoslavia escalated sharply Friday as federal army tank and artillery units moved into eastern Croatia to relieve its besieged garrisons and to crank up the military pressure on the breakaway republic.

The moves, coinciding with continued fighting along Croatia’s coastal areas, leave the latest European Community bid for a cease-fire in tatters and edge the country closer to all-out civil war.

Stipe Mesic, a Croat and the chairman of Yugoslavia’s collective federal presidency, called on federal army soldiers to stop following the “illegal” orders of their commanders, to “put down their arms and go back to their garrisons” and to “go over to the side of the people.”

He said the federal army command, starting with the defense minister, Gen. Veljko Kadijevic, had failed to follow orders of the federal presidency to hold to terms of a cease-fire, negotiated by Britain’s Lord Carrington, which Kadijevic signed Tuesday along with the presidents of Serbia and Croatia.

“It is obvious,” Mesic said, “that the army is out of control.”

Although the army declares itself to be neutral in the territorial fight between Serbia and Croatia, it has steadily intervened on the side of the Serbs. Its largely Serbian officer corps also is deeply opposed to the Croatian bid for independence.

Last weekend, under orders from the Croatian government, Croatian police and national guard units surrounded and blockaded most federal army installations in the republic, cutting off supplies of food, water and electricity. The Croatians have been buoyed by the success of the blockades, which came after weeks of military setbacks at the hands of Serbian guerrillas and national army units. More than a dozen of the smallest of these installations have now been taken over by Croatian forces.

But on Thursday, a six-mile column of tanks, artillery, armored vehicles and soldiers pulled out of the federal capital of Belgrade, headed toward Croatia.

The army columns moved through neighboring Bosnia-Herzegovina, where Muslims and Croats--traditional enemies of the Serbs--threw up barricades. Bosnia’s leaders, worried that the violence could engulf their ethnically mixed republic, ordered a mobilization of territorial reserves and demanded that federal troops “return from where they came.”

By morning, the federal troops arrived in the eastern Croatian border villages of Nijemci, Lipovac and Tovarnik, which came under attack from mortars and howitzers, according to Croatian Defense Ministry officials.

Although it was not immediately clear how much of the column of reinforcements was engaged in the battle, a Yugoslav army commander in Zagreb said it was likely that the bulk of the force would be headed toward eastern Slavonia, where the Croatian cities of Vukovar and Osijek have been under siege for about a month.

“There is a war going on in that area,” said Gen. Andrija Raseta, “so that is where I think they are going.”

There were reports of heavy rocket barrages in Osijek and Vukovar, where Croatian forces have surrounded the army’s garrisons, suggesting to some officials that a major assault could be coming.

In Vinkovci, 18 miles southeast of Osijek, defense officials said 120-millimeter shells had fallen around the local government headquarters.

Heavy fighting was also reported Friday along the coast around the strategic Adriatic port of Sibenik, where the army was trying to free its bases. Air raid alerts Friday morning sent residents rushing for shelters.

“This is the biggest fighting of the war so far,” said Branko Salej, a Croatian government spokesman. “It would seem that the aggressor has decided he wants to make a final move.”

If the army presses its assault on Osijek, Vukovar and the surrounding regions, it could slice more territory from Croatian control. Already, more than one-third of its land area is in the hands of Serbian guerrilla units, which have driven Croats from scores of villages in southern and eastern Croatia. The region includes many villages with a majority population of ethnic Serbs. Serbian nationalist fighters want to see them annexed to Serbia.

More than 500 deaths have been reported since the fighting began, shortly after Croatia declared its independence June 25. Repeated attempts at cease-fires have all collapsed virtually as soon as they were ordered. It now seems that both the Croatian and Serbian sides are determined to fight, while a worried European Community remains divided, and, so far, paralyzed over whether or how to intervene to stop the bloodshed.

The EC on Thursday decided against dispatching an armed peacekeeping force to Yugoslavia until a lasting cease-fire is in effect. About 200 EC observers in Croatia have so far accomplished little beyond noting that the cease-fires have been broken by all sides in the conflict.

Australia and Canada have urged the United Nations to dispatch peacekeepers to Yugoslavia. French President Francois Mitterrand also called for “the Security Council to intervene with its authority. It could also give a mandate to the European Community to do something.” He added: “It’s clear that these (Yugoslav) republics do not want to live together anymore. It’s important that they do not continue to kill each other, that they determine the borders and pledge to protect minorities.”

Raseta, the deputy commander of the 5th Military District that includes Croatia, spoke to reporters in army headquarters in Zagreb.

He expressed doubts similar to those of some of the European ministers about the efficacy of any foreign peacekeeping force in Yugoslavia. “Where would they stand?” he asked rhetorically. “Where is the line? Where would you deploy them?”

He blamed Yugoslavia’s political leaders, top to bottom, for allowing the conflict to get out of hand, and painted a gloomy picture of the future, should the war continue. “If serious talks are not begun immediately, I think the (final) deterioration of the situation has begun.”

He said the outcome of an all-out war would be “far from certain.” The blockade of military installations in Croatia, he admitted, has weakened the army’s position.