AT the Glina River bridge, armed farm boys are the law.It's the fourth roadblock since turning off from the main south-bound highway from Zagreb, the Croatian capital. Tractors and grain trucks block the road. A lanky youth dressed in an electric-blue T-shirt, jeans, and combat boots sticks the barrel of his AK-47 assault rifle through car windows as he checks identity papers. He and his buddies turn out to be the point men for a larger Croatian roadblock across the bridge, partially hidden in trees. The village of Glina, just a few miles away, has been the scene of bitter ethnic fighting between Croatians and Serbs in recent days. In this part of the Krajina region, many of the villages have Serbian majorities, although Croatian towns are also scattered through the verdant, rolling countryside. Tension here has increased since Croatia declared independence on June 25 along with neighboring Slovenia. Many Serbs here and elsewhere in Croatia are in open rebellion against the center-right government in Zagreb. They want no part of an independent Croatia, which they see as the reincarnation of a World War II Nazi puppet government that slaughtered tens of thousands of Serbs. Croatians passionately recite an equally appalling litany of massacre and destruction wrought by Serbs. It is an ancient feud lodged so deep that both sides see little hope of reconciliation. Outsiders quickly learn the absurdities of survival in a land where there are no blurred loyalties. A rental car's Belgrade license plates outrage a particularly baleful militaman, who shouts that the foreign occupants are Serbian terrorists as he kicks the letters "BG" (for Belgrade) with his boot. Finally, an officer intervenes. Grinning, he says the plates will pose no problem up the road. "They are perfect for where you are going. The Serbian terrorists will love you." Croatian militiamen control the north-bound roads to Glina; the Serbs, the routes to the south and west. It must have been a lovely town once, with ornate wood-frame houses and rust-tiled roofs. Federal Army troops are camped in the park now, called in to keep the two sides apart. Tanks are positioned at the town's main intersections; streets and shops are deserted. Here and there are scenes of incongruous normalcy: A wagon piled with freshly mown hay sways through town, pulled by a sputtering tractor; a woman knits in the park, surrounded by soldiers and tanks; cattle are led from pasture to barn. But the bus station has been wrecked by gunfire and the town hall pocked with bullet holes. Shell casings litter the streets. Residents have fled to nearby villages. Serbs apparently attacked the Croatian police station in Glina after Zagreb declared independence. Another clash ensued after Croatian guardsmen arrived to reinforce the embattled police station. Each side accuses the other of firing first. The tragedy of this place is that, despite the ethnic rivalries, almost everyone says he doesn't want a fight. Bojan Saban is 19, and has been a tank driver for nearly a year. "I have been lucky so far. I've never had to shoot anyone," he says. He has 50 days to go before being mustered out of the Army. Mr. Saban, a Croatian, says he would never fire on his own countrymen. "I just want to go home and stay out of all of this." As bad as Glina is, conditions are worse in the Croatian region of Slavonia, where Croatians and Serbs routinely battle each other with mortars, automatic weapons, and bombs. Homogenous Slovenia appears to be winning its struggle for independence. The battle for Croatia could be long and violent.