The border between Israel and Lebanon may be the most volatile strip of land on earth. To the north, in seemingly placid Lebanese villages, are thousands of Palestinian guerrillas manning artillery pointed at Israeli towns and settlements. To the south are outposts of Israel's armed forces, at the ready to avenge every provocation. Between them stands a 6,000-strong force of United Nations soldiers—from Holland, Fiji, Norway, Italy and seven other countries—charged with the next-to-impossible task of keeping order. The Israeli armed forces devastated the borderlands in 1978, and because of continuing guerrilla infiltration, Israeli Defense Minister Ariel Sharon recently has left no doubt of Israel's readiness to do it again.

As commander of UNIFIL (the U.N. Interim Force in Lebanon), Lt. Gen. William Callaghan, 60, has lived on the brink of war for the past 15 months. Just outside his 400-square-mile operating zone, at least a dozen Lebanese Muslim groups and eight Palestinian factions maintain army camps. Israeli-supported Christian militia south of the zone have proclaimed their enclaves to be "Free Lebanon." In recent weeks speculation has grown that Israel would use the coming of spring—and the end of Lebanon's rainy season—to launch an air and ground strike against the Palestinians. Says Callaghan wearily: "We have no enemies, only hostile friends."

The U.N. troops are permitted to shoot in self-defense, but only as a last resort. "Peacekeeping is not about firing shots," Callaghan insists. "It's about not firing—and stopping those who are." Not surprisingly, in four years they have sustained 145 combat casualties, 35 of them fatalities, while seeking to halt infiltrators from the north and south. Christian militia have mortared UNIFIL headquarters twice, destroying several helicopters and severely damaging buildings on the base. "We must look for trouble at the four points of the compass," says Callaghan, "and then we look behind our backs."

For all the pressures, Callaghan—his sky-blue beret at a tilt, a swagger stick tucked under his arm—remains unflappable. The 43-year veteran of the Irish military is referred to as "Boss" by his polyglot U.N. troops, most of whom serve six-month tours. Leading an international force presents special challenges. Callaghan caters to his troops' varied national origins by joining in barracks-room bashes that range from Italian pasta nights to Fijian sword dancing. Still, in professional terms, he says: "Soldiers speak a common language."

His polished diplomacy and adroit use of blarney have gained Callaghan rapport with virtually every party to the conflict around him. During one recent meeting, for example, PLO officials railed at reports that the Israelis were stocking crocodiles in the Jordan River; the Arabs saw in the move a sinister plot to devour infiltrating terrorists. Callaghan listened patiently, then encouraged the Palestinians to breed their own reptiles. "Ours will be victorious," a guerrilla chief boasted. "No," Callaghan replied, "yours will mate with the Israelis' and that will be your contribution to the peace process."

That unorthodox approach to negotiations (he once dispatched cases of Irish potatoes to Israeli Lt. Gen. Rafael Eitan as a peace offering) has earned him regular appointments with the ranking figures on both sides, including PLO chairman Yasser Arafat and Israeli Defense Minister Sharon. "People see Callaghan for what he is," observes a Western diplomat in Beirut. "He is not a young officer out to make a name for himself, but a seasoned general at the end of his career whose only motive is his devotion to his U.N. mission."

That devotion has allowed the general only one brief visit to his home in Ireland since he began his open-ended tour of duty. Nor has he had much time to use the beach house he rents in Nahariya, Israel, a few miles from the base. His wife, Carmel, divides her time between Dublin and her husband's posting. "It takes a very special woman to be a soldier's wife," the general says. "She accepts the rough-and-tumble as it goes." So does the general, who quotes Shakespeare with a thespian's verve. But these days he laments, "I've no time to read it anymore, just to remember."

Growing up in a large farm family in County Cork, Callaghan chose soldiering at 17, winning a cadet's appointment to the Irish military academy. While rising steadily through the ranks, he spent six years in U.N. peacekeeping operations in Israel, the Congo and Cyprus before beginning his current stint, and still holds the title of adjutant general in Ireland's forces.

Callaghan maintains he learned as a father the skills he now finds so useful. He and Carmel have five daughters and two sons, ages 19 to 36. "Rearing a family is about negotiations, after all," he says with a grin. "You've got to listen to all points of view, and then you have to make your decisions impartially. Probably the most difficult step is making children understand your decision is fair and final." He pauses, then adds: "The sides here are somewhat the same."

His patient evenhandedness was instrumental in establishing a cease-fire last July in southern Lebanon, a tenuous peace that endures despite periodic breaches. Land values have tripled in the area, and the population, which fell to 500 in 1978, has risen to 250,000 civilians. "Peace begets peace," the general argues. "Suppose a family here has been pinned down by fighting. One day the shooting stops. They can get up, go for water and look after the sheep. They can do this for one day, then miraculously the next and the day after that. Pretty soon it's something they demand." When he is reminded that rumors of war are everywhere around him, Callaghan turns his gaze to the Amel Hills near his office, where the red poppies are now ablaze. "Look at the peace that has been established here," the general says softly. "It would be a pity if this were undone."