EVERYTHING in Belgrade seems at a turning point: politics, the civil war with Croatia, the economy, the federal Army, people's lives, history.Other than the 75-car gas lines and the occasional Soviet-made M-48 tank rumbling north down the highway, though, very few surface clues hint at the tensions beneath the surface of this ancient Balkan city. In the midst of another muddled cease-fire, the Serbian capital is a complex city of unanswered questions. Shops are full. The annual Miss Yugoslavia pageant is in full swing. But only 50 miles away, a grim struggle may resume at any moment. The war, too, is complex. It is a civil war between the federal Army and the breakaway republic of Croatia. It is an ethnic war between Serbs and Croats. It is an ideological war pitting fiercely Marxist Army generals against Croatian nationalists. It is a religious war between the Orthodox Serbs and the staunchly Roman Catholic Croats. The war has released some of the most deep-seated hatred and strife in the Balkans. It threatens to spill into the republic of Bosnia-Herzegovina. Four Serbian regions in Bosnia-Herzegovina have declared autonomy in less than a year - two in the past week. Pro-Serbian federal troops from the republic of Montenegro marched into Bosnia-Herzegovina Sept. 22, wreaking havoc. Yet at bottom, say Western diplomats and many Serbs here, the war is a manifestation of Serbian President Slobodan Milosevic's push for a "Greater Serbia." Zdelko Simic, special adviser to Mr. Milosevic, strongly rejects these claims. Serbia is only interested in two principles, he told the Monitor: self-determination for Serbs in Croatia, and their right to vote on borders. But who decides borders? A map has been circulated in Belgrade shading places where it says Serbs are a majority. Most of Croatia is covered, leaving only a sliver of space around Zagreb. Western diplomats say the map is "pure fiction." One observer notes that this could indeed be a map of the Serb majority - if the federal Army succeeds. When asked if this map was a fair outline of the areas of Serbian self-determination, Mr. Simic answered "yes." Budimir Kocutic, vice president of Serbia, argues that the internal borders of Serbia are false, made after World War II by President Josip Broz Tito, a Croat. Milosevic does not talk of a Greater Serbia publicly. Officially, the civil war is a federal Army matter with which the Serbian government has no connection. Yet testimony linking Milosevic to the Yugoslav Army has come from Yugoslav Prime Minister Ante Markovic, who has been marginalized by the politics unleashed in Yugoslavia since Slovenia and Croatia declared independence June 25. In a closed executive council meeting last week, Mr. Markovic spoke of Milosevic's plan as "a program of Greater Serbia." In minutes of the meeting published by the independent weekly Vreme, Markovic accused federal Army leader Gen. Veljko Kadijevic of treason. Markovic also said he had heard tapes of Milosevic ordering the federal Army, through Radovan Karadzic, leader of the Serb Party of Bosnia-Herzegovina, to give arms to the Serbs in the republic's autonomous Krajina region. The treason charge against General Kadijevic was based on evidence Markovic said he had that Kadijevic conducted meetings in Moscow on March 19 with then Soviet military leader Marshall Dimitri Yazov. Markovic said he "had not been informed"of the meetings. On Monday, the Army newspaper called the charges "slander and insinuations against the Yugoslav Army and its innermost leadership." In Belgrade, the war is not popular. An independent poll last week found 80 percent of people in Belgrade opposed to the conflict. "How much am I willing to sacrifice for a Greater Serbia?" asked one young man hiding from the Army. "Not much." The views in the countryside are different. There, no alternative news is available and the programs of Milosevic are popular. The common Serb supports Milosevic, because he was the first communist to stand up for Serb rights. Perhaps the saddest voices in Belgrade are those of liberal moderates who say often that the "space" for free speech and thinking is being inexorably reduced. For them, a federal Yugoslavia was the ticket for Serbia to surpass its historic nationalism and enter "the wider community of Europe and the world," says Pavle Petrovic, an economist at the university here. Europe now beckons in a different way. As one young Serb intellectual states: "Most of my friends have left. It's getting bad. I know two microbiologists who are washing dishes in Amsterdam." The most acute complaint among liberal Serbs is state control over news media. Croatian TV and radio have been jammed. There have been editorial staff purges in Serb TV, radio, and newspapers. "In the 1970s papers tried at least to get close to the truth," Dr. Petrovich says. "But now lying doesn't matter. It is almost impossible for the truth to go through." Three important questions remain: * How far will gas reserves go? This war requires 150,000 tons of oil a day. Serbia's fallback has been Soviet fuel. Yet the United Nations or the European Community may exert pressure on Russia to reduce the flow. * Will relations between Milosevic and the Army stay strong? The two interests - Serbian nationalism and Marxist self-preservation - have been separate but parallel. Some observers see fissures. * Will the 2.5 million Albanians in the Serbian province of Kosovo arise? This would create an entirely front for Serbia.