Peacekeepers win Peace Prize. The UN's peacekeeping forces have won the 1988 Nobel Peace Prize. Their tough job is illustrated by UNIFIL, the force that patrols explosive south Lebanon.

The blue-and-white UN van turns east off south Lebanon's coastal road toward Checkpoint 1-1. The khaki-clad military commander stops and points to a dozen new buildings. ``Five years ago people were trying to get out of here,'' says Lt. Col. Matt Sarasau, commander of one of the nine foreign infantry battalions that make up the United Nations Interim Force in Lebanon (UNIFIL). ``It's a measure of the degree of security people feel that they're now moving down south.''

For bringing a measure of security to war-torn south Lebanon, UNIFIL yesterday shared in this year's Nobel Peace Prize, awarded to the UN peacekeeping forces. Seven such multinational contingents are deployed along volatile in the Middle East, Cyprus, and the Asian subcontinent.

On the face of it, UNIFIL seems an unlikely candidate to share the prize for peacemaker of the year. Its mandate, spelled out in a 1978 UN resolution, is no closer to being realized today than it was when the 7,000-member force was installed after Israel's invasion of south Lebanon in 1978. Israel remains in control of large tracts of southern Lebanon; hostilities occur in the area almost daily; reestablishing the authority in south Lebanon of the weak and now-divided Beirut central government seems out of the question.

Still, the $150 million per year invested by the international community in UNIFIL has paid off, says Colonel Sarasau, whose 700-man battalion of Fijians patrols the coastal region south of Tyre.

Ten years ago, scarcely 10,000 people lived in the war-ravaged quadrant north of the Israeli security zone and south of the Litani River, which constitutes UNIFIL's sphere of operation. The area has been battered by the country's 13 years of civil war, and Israeli invasions in 1978 and 1982.

Today, the area is more stable than much of the rest of Lebanon. The migration triggered by years of conflict has been reversed. Swelled by the return of Lebanese workers from Beirut and the Gulf, the population has quadrupled, spawning a minor construction boom.

Whatever credit UNIFIL can claim for the turnabout owes little to force of arms. The light weapons used by UNIFIL soldiers can be used only in self-defense. Like other UN peacekeeping forces, UNIFIL has had to rely more on wits and moral authority than on brawn.

Instead, success has been the product of a discreet pattern of cooperation that has evolved between UNIFIL and Amal, the 17,000-man Shiite Muslim militia that has become the de facto government in south Lebanon.

Fearing Israeli reprisals, Amal has been a force for stability in southern Lebanon, thwarting attempts by local Palestinians and the pro-Iranian radical Hizbullah from using south Lebanon as a corridor to attack Israel. Amal's efforts have been abetted by UNIFIL's network of observation posts, checkpoints, and roving patrols, erected to stop the movement of armed people across the UN zone. Violators, UNIFIL sources say, are routinely turned over to Amal.

``Without UNIFIL here it would be impossible for Amal to control the area,'' says one longtime UNIFIL official. UNIFIL's cooperation has produced a reciprocal loyalty that, until now, has provided a measure of protection to its contingents. UNIFIL officials fear that recent gains could be offset by last week's assassination of a top Amal official, and open the door to renewed Palestinian and Hizbullah attacks on Israeli positions.

Since 1978, 156 UNIFIL members have been killed and 230 wounded in the cross fire between Lebanese and Israeli fighters. Last February, US Marine Lt. Col. William Higgins, who headed a 76-member observer group attached to UNIFIL, became the ninth American to be abducted in Lebanon.

WHERE THE UN KEEPS PEACE (UNTSO): UN Truce Supervision Organization Operates in Israel and four Arab states; reports on hostilities. Cost: $20.3 million (1988) Troops: 298 (UNDOF): UN Disengagement Observer Force supervises cease-fire between Israel and Syria. Cost: $34.7 million (1988) Troops: 1,327 (UNIFIL): UN Interim Force in Lebanon patrols buffer zone in south Lebanon, to prevent fighting between Israeli and Lebanese forces. Cost: $139.4 million (1988) Troops: 5,850 (UNFICYP): UN Peacekeeping Force in Cyprus patrols buffer zone to prevent Greek-Turkish Cypriot clashess. Cost: $25.2 million (1988) Troops: 2,122 (UNMOGIP): UN Military Observer Group in India and Pakistan supervises cease-fire. Cost: $3.7 million (1988) Troops: 39 (UNIIMOG): UN Iran-Iraq Military Observer Group aims to establish cease-fire line, arrange troop pullback to international borders, monitor cease-fire compliance. Cost: $37.5 million (for first 3 months) Troops: 350 observers; 400 support military (UNGOMAP): UN Good Offices Mission in Afghanistan and Pakistan monitors Geneva pullout accords. Cost: $7 million (1988) Observers: 50