Israeli-backed Christian militiamen shelled a U.N.-policed vilage in south Lebanon today, wounding an Irish peacekeeper, three Lebanese women and an 8-year-old boy. Timur Goksel, spokesman for the United Nations Interim Force in Lebanon, said the Irishman was injured in the head when a 60mm mortar round crashed into one of the Irish battalion posts in Qabrikha, 18 miles east of Tyre. He declined to give the Irishman's name. Lebanese police later said four villagers, including three women and a boy, also were wounded in the bombardment. Police said the South Lebanon Army militia opened up on the Shiite Moslem village after a roadside bomb exploded in the village of Qantara, in Israel's self-designated securitu zone in south Lebanon. It as not clear whether anyone was hurt in the explosion. The 2,000-man militia patrols the 6-to-10-mile deep security zone jointly with Israeli troops. The buffer was established after Israel withdrew the bulk of its occupation force from south Lebanon in 1985, ending a three-year invasion.