EVERYTHING looks calm outside the main federal Army headquarters.There's no military traffic visible, only civilian traffic, trams, and cars. Children play and laugh. Parents relax. But the future of the July 7 cease-fire remains unclear. Yugoslav leaders yesterday accused Slovenia of breaking the peace accord by not allowing all federal Army troops to leave, and there were reports of renewed fighting between Serbs and Croats. Here in the Croatian capital, no one has forgotten the events of last week. When troops and tanks tried to move out of the Marshal Tito barracks, an angry crowd threw bottles and rocks - and some say, fired rifles at them. What happened next, no one disputes. Soldiers opened fire and killed several residents. "I'm frightened by the shootings," says Kosta Tomasevic, a draftee from Bosnia with small, delicate wire-rimmed glasses. "This nation is against us." As the Yugoslav crisis unfolds, the 180,000-man federal Army will play a crucial role. After Slovenia declared independence, federal troops, including the troops from these barracks, attacked. Tanks and armored personal carriers moved to secure border posts. Federal jet fighters, firing air-to-ground missiles, strafed the main airport outside Ljubljana, the Slovenian capital, and destroyed a television transmission tower. But the 40,000-man Slovenian militia routed the Army. With only light weapons, Slovenian fighters stood their ground and erected barricades of trucks and cars to block the tank movements. Scores of soldiers were killed, wounded, and taken prisoner. Under this week's cease-fire accord, the prisoners have been released and the Army has retreated to its barracks. But both Slovenians and Croats fear the federal Army may once again try to crush their independence movements. Leaders of the rebellious republic accuse the Army of being controlled by Serbs. About 60 percent of the Army's officer force is Serbian, and Croatian leaders say the Army is supporting Serbian militiamen in clashes against Croatian militiamen. "The Army is a Serbian instrument," says Croatian Defense Minister Sime Djodan. "It wants to restore a Stalinist, centralized system over all of Yugoslavia." A visit to the Marshal Tito barracks illustrates the tensions tearing apart the Army. The military was long thought to be a unifying force in Yugoslavia, because it brought together recruits from all across the country. But now that very diversity creates problems. Consider draftee Boris Lovric. The private is a Croat doing his year-long Army service in Croatia. That meant last week he faced off against fellow Croats. "They didn't believe me that I'm Croatian," he recalls. "They thought we were Serbian here and they were very angry at all of us." Many draftees like Private Lovric are deserting. In many cases, mothers have come to the bases in search of their sons. Relations among the different nationalities on the base seem good. Edvard Lestamic, a Serb, sits next to the Croatian Lovric. The two friends agree. "There's no nationalism here," says Mr. Lestamic. "He comes to my house in Belgrade, I go to his house in Zagreb." Col. Andrija Kovjic, the commanding officer, intervenes. The Army wants peace, he says. When it sent troops to Slovenia last week, it just wanted to ensure the integrity of Yugoslavia's borders. If it really had wanted to crush the rebellious republic, the colonel says it could have easily done so, using overwhelming firepower. "The Army isn't just made up of unreconstructed Communists, and it doesn't fight for Serbia," he says. "We would never go against the wishes of the local populations. After all, would the American Army ever occupy Texas?" Croatian officials say large segments of the Army are moderate and working to prevent a civil war between Croats and Serbs. "There are troops that want peace and are willing to help us," says Mario Nobilo, a Croatian presidential adviser. "But there are also generals who dream of a greater Serbia." Among the Croatian public, there are few doubts: The Army is seen as a homogeneous, sinister force. Residents living across the street from the Marshal Tito barracks were shocked by last week's violence. "If this Army stays here," says Nina Cviiko, "there'll be war."