THE cease-fire in Yugoslavia for the first time seems to be holding for more than a few minutes around the sites of the heaviest fighting in eastern Croatia.However, informed sources here in the Serbian capital say the cessation of hostilities, negotiated Sunday between Croatian President Franjo Tudjman and federal Army chief Veljko Kadijevic, is due more to the strategic weaknesses and physical exhaustion of the two sides than to any high-minded desires for peace. "Both sides need a breather," says Milos Vacic, military analyst for Belgrade's independent weekly newsmagazine, Vreme. "They need some time to put order and discipline back into their ranks." Reports from the field point to general chaos and lack of morale in the Serbian-led federal Army, which has been fighting on the Serbian side in the name of a federal Yugoslavia. Trouble has spilled over into Bosnia-Herzegovina, where Deputy Prime Minister Rusmir Mahmutcehajic said the situation was "dramatic." Federal troops moving through the republic toward Croatia have been blocked by local Muslims and Croats who accuse the Serbian-led Army of trying to crush Croatia. Belgrade independent radio reports numerous desertions by federal Army troops and a problem recruiting and calling up reservists. Army recruiters in one case swept through the downtown McDonald's restaurant asking young men for identity papers. Federal Army troops now come almost exclusively from Serbia. On the Croatian side, journalists returning from the field report that the Croatian national guard has limited numbers and is very inexperienced as a fighting force. General Kadijevic has announced that he is prepared to liberate "by whatever means necessary" a dozen federal Army barracks surrounded by Croatian national guard forces and cut off from food, water, electricity, and communications. Croat forces with only light weapons could face an all-out armored and Air Force attack, which would certainly involve action in major urban areas such as Zagreb. The cease-fire terms allow food and water for the Army troops - a significant concession by Mr. Tudjman. Croatian radio said the Yugoslav Navy had lifted a week-long blockade of key ports on the Adriatic coast, although a blackout remained in force in Split as a further precaution against snipers. Europe's wariness about sending a peacekeeping force to mediate a hot Balkan ethnic war has hurt Tudjman. German sources here say that German Foreign Minister Hans-Dietrich Genscher has at least temporarily backed away from his push inside the European Community to give recognition to the breakaway republics of Croatia and Slovenia. "This has been a very high-stakes game," says one Serbian intellectual. "Tudjman has been counting on the West and the EC to jump in on his behalf. Now he sees he won't get this. He miscalculated." However, fresh analysis of the condition of the federal Army indicates there is plenty of miscalculation on all sides in the Yugoslav civil war. That Croatian forces suffer from a lack of discipline and strategy does not surprise anyone. The Croatian forces were established barely a year ago. Problems of the federal Army, which appear to be broader and deeper than have been previously reported, have been of more concern here this week. The Army, which has trained for 40 years as a defensive Army, is now engaged in an internal war. Mr. Vacic says the Army has not been prepared to conduct such a war, either logistically or strategically. "The federal Army has underestimated the situation," he argues. "They have overreached. They have sent forces across Croatia, and now they face classic problems of resupply in terms of food and fuel. They need a Ho Chi Minh trail, but don't yet have one." Yesterday, Reuters reporters around Shibenik on the coast said the federal Army there was in some disarray and possibly on the verge of losing. Morale is low, according to one reservist just back from the front who was reclassified as a "volunteer" and kept in the Army a month longer than legally required. Mutinies have been reported reported both in Slavonia and in camps in southern Serbia, usually an Army stronghold. Some of the mutinies are by Serb peasant boys who are traditionally good fighters but who "don't like to go too far from home," as a young Serb here noted. Reports on recruiting in Belgrade suggest as many as nine out of 10 young men are not answering the call. One young man in Belgrade who claims he is hiding from the federal Army, says half the Army-age youth in town are "sleeping in different places and avoiding the Army." Milos, 22, interviewed while waiting to see "Terminator 2," the new Arnold Schwarzenegger film, said, "We should let Croatia go. I was happy before. I don't want war, I just want to be like other kids my age in England, France, and Germany." Thus far, neither the Serb territorial defense, the Croats, or the federal Army appear ready to back down. The Army is one of the last serious Marxist organization left in Eastern Europe. It will not give up easily, says one high-level Serbian source, who adds, "The role of the Army in a communist society is not well understood in the West. Our Army makes the Prussian military look like a kindergarten."