One week after Israeli invaders ended a three-month occupation of southern Lebanon, their Christian allies here appear to be split.

Staged or for real, the differences in the southern Christian camp have done little to ease a potentially explosive stalemate over who has authority in the area.

Involved in one way or another are the Christians, the weak Lebanese government, the Palestinian guerrillas, the 6,100-man U.N. peacekeeping force, the Israelis and the Syrians.

The Crux of the problem was voiced by a grizzled Christian militiaman in an Israeli-supplied uniform who prevented reporters from approaching Marjaoun, the center of the eastern-most Christian sector theoretically commanded by Lebanese Army Maj. Saad Haddad.

With every evidence of real anger, be insulted principal Lebanese Christian deities& Phalangist Party leaders Pierre Gemayle, his son, Bechir, Haddad, and especially his nominal deputy, Maj. Sami Shidiac, commander of the Christian sector in the southwest.

"To hell with them all," the militiman said, "especially with Shidiac and Haddad, the dirty defeatists who are taking orders from Beirut and selling us out."

His anger appeared to substantiate a version of events in Marjayoun that suggested the militiamen there had revolted against Haddal for accepted Lebanese army orders to confine the regular troops to barracks and cooperate with the U.N. forces.

A different version in Beirut insists that Haddad and the militiamen are staging an Israeli-encouraged charade to prevent UNIFIL - as the U,N. expeditionary Corps is called-from occupying positions in an approximately 4-mile-deep area along the Israeli border.

Adding to the confusion is a rivalry between Haddad and Shidiac, who is his Ain Ebel headquarters 10 miles further west appeared to be in total control of his militiamen.

What emerged as a common denominator, however, is the Christian's fear of abandonment now that the moment of truth has come. For 18 months they relied totally on Israeli protection.

Shidiac, an amiable, red-bearded rareer officer, echoed this angluish in a three-hour conversation interrupted by radio conversations in Hebrea with the Israelis, in French with Phalange headquarters in Beirut and in Arabic with his Lebanese Army superiors.

Dressed in blue jeans and sports shirt, a sign that he was obeying army orders confining him to barracks, Shidiac blamed Prime Minister Selim Hoss for "sabotaging" a compromise deal with the United Nations.

Caught embarrassingly in the middle, the United Nations officially is on record as saying it "prefers not to talk on a day-to-day basis". That formulation means the United Nations is counting on behind-the-scenes diplomacy - especially American pressure on Israel - to bring the Southern Christians to heel.

Last week, Hoss denounced an agreement reached between Shidiac and the United Nations for partial UNIFIL deployment in the Christian area on grounds that the major did not represent legitime Lebanese authority. Syria, the Palestine and Lebanese leftists have charged Shidiac and his men were "traitors" for dealing with Israel.

Arguing that at least his forces deserved "parity" with their arch-enemies, the Palestinian guerillas, Shidiac said, "This is a Kafkaesque situation. Here I am an officer of 20 years' service accused of not representing Lebanese authority when they deal with (overall Palestinian commander) Yasser Arafat, who has been trying to undermine Lebanese soveighty for years."

If Hoss wants UNIFIL in my area, UNFIL must first deal with us," he insisted.

He seemed to be hinting that he might sweeten terms governing a U.N. presence although he insisted that it was "not part of the UNIFIL mandate to take over the Christian enclaves."

Those enclaves from the superstructure of the entire Christian-controlled border strip, much of it inhabited by Shiite Moslems.

Shidiac recalled that the United Nations had negotiated with the Palestinians, who first resisted before accepting a compromise arrangement virtually removing their armed presence south of the Litani River. He appeared genuinely concerned lest the current "dialogue of the deal" degenerate into shooting incidents between his men and the United Nations.

His regular troops risk no longer being able to exercise the "moderating influence" of professional soldiers on the militiamen, who are "enjoying their power" and "don't give a dawn about world public opinion," said Shidiac.

By most accounts, the regular troop's strength in the south is approximately 600. There may be as many as 800 millitiamen in various organizations. All these forces are supplied, armed and otherwise supported by Israel.

Most observers now despair of ever seeing long-discussed moves by the Beirut authorities, that is, sending fresh and partially Moslem units to the south and replacing Shidiac and Haddad with other officers.

But the government has sought to advertise its presence now that the 18-month Palestinian blockade of the Christians in the south has been lifted. The first two gasoline tank trucks were in Ain Ebel yesterday as were repairmen working to provide electricity once again. Villagers happily reported the arrival of Lebanese goods which they said were half the price of Israeli equivalents purchased throught the so-called "good fence" allowing free access to the Jewish State.

During their three-month occupation, the Israelis built fortifications but also strategic hardtop access roads throughout the border area and opened up new "good fences" opposite Shiite villages to complement those for the Christians.

Still, Shidiac and all the Christians are terrified lest UNIFIL finally take over security. Shidiac insisted that the United Nations could not be trusted and said UNIFIL had left as many as 600 Palestinian guerillas back south of the Litani River.

He kept repeating that Israel could not afford to sell them out. "TThey can't drop us," he said, "because in Israel public opinion exista - it isn't Syria - and backs us. If the politicians dropped us, the Begin government would fall."

Whether he really believed that was unclear, however, "We had no choice," he said. "It was either Israeli help or genocide at the hands of the Palestinians."

Musing out loud, he added, "I have been wounded three times in this war. I have sacrificed my career. I will have no place in the new Lebanese Army. I did my best, but I fear it was all for nothing."