AQIA BRIDGE, Occupied Lebanon – On the southern approach to this bridge over the Litani, in the hollow of eight green hills, the Iranians are preparing for evening, stacking sandbags around their sentry posts.

"There, behind, another row," directs an officer. And over there, too."

Soon it becomes apparent that the sandbags are being stacked to protect against fire that could come from across the bridge, where the Palestinian Fatah control the hills; or from the no-man's land on either side, or from the rear, where the Israelis have staked out their lines.

The officer is asked where he expects the trouble to start.

"Everywhere," he says. "We have no friends."

It is a comment heard at a dozen United Nations positions in the belt just south of the Litani River, the new buffer zone manned by peacekeeping troops.

The Palestinian commandos are just to the north, some of them apparently uncontrolled by the Palestine Liberation Organization (PLO), which has endorsed the cease-fire in south Lebanon.

To the south stand the massive forces of the Israelis, a disciplined army also committed to the cease-fire but not openly confident of the U.N.'s ability to fight off a Palestinian advance and not necessarily likely to let U.N. forces deal with major trouble in their own way.

And in some spots, between the U.N. troops and the Israelis, stand the right-wing Phalangist Lebanese, who greeted the first groups of U.N. soldiers with bursts of machine-gun fire. The Phalangist Christian militiamen are still hostile to the U.N. presence here and as trigger-happy a group as any in the Mideast.

At this bridge over the Litani, the small river behind which the Palestinians retreated from last month's Israeli assault, there has been no shooting.

From the Israeli lines, the road winds down over hills almost perfectly round, from tops of sandpaper gray through ancient and cunning terrace work to fields of green velvet and orchards below.

At sunset, there is the song of birds on the hills, mingled with the rush of white water in the river and the sad, soft strains of a flute from the little Iranian camp. The failing light fades the sky from brilliant blue to a misty grey, and the hillsides, splashed since dawn with wildflower pastels, darken first to mauve, then to blue, and then to solid black.

Only up close does the ugliness crowd in: a twisted, burned Jeep and shrapnel in the road; the deep wound of a bomb that has carved a gash of red brown dirt, the color of dried blood, in a bright green field; six cows, and a bull lying dead on the road, stinking and bloated and buzzing with a million flies.

With the ugliness comes the fear.

"Yes, it is beautiful," the young Iranian says. "Beautiful and dangerous. That is what Lebanon is for me."

He is a lieutenant, lately promoted, serving a compulsory two-year army hitch. He doesn't want to give his name. At 25, with two sons at home in the north of Iran, he can think of a few places he'd rather be.

Most of the U.N. troops from France, Sweden and Norway are career army men who volunteered for the change of pace and the extra pay that U.N. duty affords.

Not the Iranian contingent.

"Yes, of course," says the Iranian with a wry smile. "We had the choice, too. I chose because my commander told me to choose."

He says he is uncertain why Iran or his unit was picked to stand in the buffer between or amid Israelis and Phalangists, Palestinians and a smattering of Lebanese national forces, and the Syrian troops who make up the bulk of the Arab League peace-keeping forces farther north of the Litani.

"How do I know?  My commander said we are going," 4,000 U.N. troops stationed in the hills of southern Lebanon.

The Israelis, who reportedly used 20,000 men to conquer the south in six days, are slowly withdrawing as the U. N. force swells to full strength. There is no formal timetable for full withdrawal, according to Israeli spokesmen.

"It depends on how quickly the U. N. force settles in and the situation settles down," an Israeli Defense Forces official says.

"And I wouldn't be surprised to see our men retain their positions just north of the (Israeli) border for a considerable time, just to make sure we won't have any more trouble on our hands."

Deployment a question

The schedule for U.N. deployment is only one of a number of questions that remain to be sorted out in southern Lebanon.

Foremost, in the minds of the soldiers, is the attitude of the Palestinians and the Christian Lebanese who have been battling in these hills for two years.

Yasir Arafat, head of the PLO, has announced support of the cease-fire. On the other hand, he says he will not cease attacks on Israeli forces elsewhere. And Palestinian guerrillas who do not recognize Arafat's leadership are expected to do all they can to sabotage the cease-fire.

The Phalangists, nominally cooperating with the Israelis in the maintenance of the cease-fire, actually have staked out a small enclave of their own in the eastern portion of south Lebanon. In this area, they reign by machine gun, with little heed for the Israelis.

An Israeli spokesman in Metullah said, "That is their area. We can't tell them anything about what to do in there."

A Swedish U. N. officer in the same Israeli border town said, "They're supposed to be the Israelis' headache, but they've been nothing but trouble to us."

There is also a question about the area the U.N. forces are supposed to control. They are solidifying their hold on a belt along the Litani from the Christian-held area in the east, around Marjayoun, almost to the Mediterranean coast in the west.

But the U. N. forces have not taken control of Tyre, the Lebanese port city still in the hands of armed Fatah commandos driven there by the Israeli assault.

U. N. soldiers, asked about their plans for Tyre, say it is a matter for political and not military decision. "Im sorry to tell you I just don't know," says Swedish Major Jan Thunstrom, at the head of a reconnaissance column in Deir Ayya. His answer bears a trace of asperity: "I'm afraid you'll have to ask New York."

Maj. Gen. Emmanuel Erskine of Ghana, head of the U. N. forces in southern Lebanon, says in an interview that Tyre will have to remain a question. He complains of the "insufficient mandate" his soldiers have. "We are not allowed to disarm the great number of armed men still operating in the south," he says.

But Erskine has been at pains since he arrived to answer the major question about the U. N. forces in south Lebanon: Will they fight?

He is asked what hs forces are supposed to do if the sporadic firing they have faced does not stop.

"They'll fire back," he says sharply. "We are going to control. We are going to function under maximum restraint, but we will control.

"This is going to stop," he says. "And it will, because we have the mandate. We have some weapons and we will use them."

Not everyone is equally convinced.

"They're like a stage set, like the movies," says one Israeli officer. "Like in Hollywood, where you see the whole town, but if you push on the wall there's nothing behind it and it just falls over."

The Israelis were not reassured by one of the first confrontations, last week, when a Swedish force moving toward the Khardala Bridge over the Litani turned and retreated from Palestinian fire, leaving its Israeli escorts to fire back at the Fatah gunners in the hills.

After one Swedish soldier was killed and another seriously wounded by a land mine, a half-dozen members of the Swedish contingent asked for transfer back to the drearier, but safer, confines of the Sinai Desert.

This week, a brand new Norwegian troop just arriving at the same Khardala Bridge, was shelled by mortars, apparently from Palestinian positions above, without firing back a single shot.

"You have to understand," says a Norwegian major, Hans Haug, "that we are not supposed to get into a battle situation. This was one of the conditions of the Norwegian government."

Haug is asked what the Norwegian troops are supposed to do, if not to do battle. "Our main job right now," he says, "is to prove to everybody that we are neutral – no sympathy to any of the conflicting parties."

At the bridge, the Iranian lieutenant puts it more tersely:

"We can have no friends. That is not what we are here for. Palestinians, Israelis, they are all the same to me. I do not care about any of them."

The most perplexing question of all confronts the U. N. troops in this beautiful and dangerous land: What are 4,000 apparently sensible men doing playing human shock absorber between parties for whom they care scarcely at all?

"My commander ...," the young Iranian begins, but that has been heard before.

"We have to trust in the U. N.," says Maj. Haug, 38, who describes himself as a bit of an idealist. "We are in Norway a small country. We know we cannot do it alone. If we can put a little strength in the U.N., it's good for us. And I know it's high dreams, but if you could get a kind of world government, where people trust each other, people settle down, it might be a better world."

"It's a job," says Folke Carlsson, master warrant officer in the Swedish contingent. Carlsson, 42, has been at it for 22 years. The skin around his little blond mustache and big blue eyes shows a network of wrinkles, finer and more detailed than the Israeli maps of Lebanon.

"And it's some excitement, too," he says. "I've been out before. The Congo in 1960."

He is asked which was tougher, Lebanon or the Congo.

"The same," he says. "They're all the same ... The Phalangists, the Palestinians, the Israeli, the Syrian. Nobody can really understand this situation. I cannot.

"But it's a job. It's understood. You make them stop shooting."