NATO-LED TROOPS CAUGHT IN BATTLE OVER KOSOVO TOWN
French troops kill Albanian gunman as fierce fighting continues in streets of Mitrovica, Kosovo, in most sustained clashes involving NATO peacekeepers since arrival in June 1999; more than dozen people are wounded, including two French soldiers, and 17 are arrested; French, Italian and British troops come under fire from snipers; former commander of Kosovo Liberation Army says Serbs attempted to attack Albanian area and that fighters of outlawed guerrilla force fought back to defend it; both Serbs and Albanians regard Mitrovica as last battlefield in war for Kosovo; thousands of Albanians, still unable to return to homes, consider Mitrovica last place still to be liberated from Serbian persecution; Serb community leader blames Albanians; both sides accuse other of wanting to control area beacuse of presence of iron ore and precious-metals mines; photos; maps (M) (M)