What next? That is what Israelis are asking about their Army in Lebanon after its partial troop pullback to south Lebanon and about the future leadership of their government.
In both cases, it would help to have a crystal ball.
The long-awaited Israeli pullback this past weekend of thousands of men, tanks, and vehicles from Beirut suburbs and the nearby Shouf mountains was remarkably orderly and casualty-free. But Israel must now worry about how to keep Syrian forces based in Lebanon from moving into the area and about how to respond to an explosion of Lebanese communal violence between Christian and Druze militias in the areas Israel has evacuated (see related story, Page 17).
At home, Israel faces an unusual vacuum of leadership. Despite Prime Minister Menachem Begin's announcement Aug. 29 declaring his intention to resign, he still has not formally tendered his resignation to President Chaim Herzog. He apparently will not do so before the coming weekend, the Jewish New Year holiday.
The reason: His would-be successor, Foreign Minister Yitzhak Shamir, newly chosen as head of Mr. Begin's Herut Party, is having trouble pinning down support from all members of the existing government coalition. He had wanted to be able to tell the President that he could immediately reconstruct the same government.
Meanwhile, the opposition Labor Party is trying, against stiff odds, to woo away enough doubters from the government coalition to gain a majority in the 120 -seat Knesset, or parliament.
The Lebanese fighting is overshadowing the maneuvering for a new government. Israeli Defense Minister Moshe Arens bluntly warned the Syrians not to get involved, saying Sunday, ''We do not want Syrian forces entering the areas we leave, and I think that message is understood.''
Israeli strafing on Sunday of Syrian tanks manned by Druze fighters on the Beirut-Damascus highway near Bhamdun was seen as a clear warning of the possible consequences to Syria if it should intervene. A senior Israeli official said Monday that a Druze victory for the battle for Bhamdun would strengthen the Syrian position. He indicated that the potential loss of Bhamdun was seen by the Israelis as crossing a red line, but he did not say what they would do about it.
At the same time, Mr. Arens played down Syrian involvement in the current clashes. He said that while Druze militias may have receYved Syrian equipment to fight the Christians, ''there was no direct Syrian involvement in the fighting on Sunday'' to the best of his knowledge. (Lebanese state radio reported on Monday that Syrians and Palestine Liberation Organization forces had been sent into the area evacuated by Israel to back the Druze militias.)
Mr. Arens would not respond to questions about the Israeli response if the Syrians moved into the Shouf. But he said, ''I would be very surprised if they tried.'' One Israeli expert on Syria expressed doubt that the Syrians would ''rush in'' to the disputed areas.
Mr. Arens told journalists that the situation in east Lebanon's Bekaa Valley, where Israeli troops face Syrian troops, was ''no more tense than it had been in past periods.''
Israeli officials are disturbed by the statement from Lebanese Prime Minister Shafik Wazzan that last May's withdrawal agreement between Israel and Lebanon is ''now as good as frozen.'' Observers in Beirut have been speculating that Lebanese President Amin Gemayel might suspend the pact in order to pacify hostile Muslim factions inside Lebanon.
Moreover, the weakness of the Lebanese government and its inability to send the Lebanese Army into Israeli positions evacuated in the Shouf hold out little hope for an early Israeli departure from south Lebanon. Mr. Arens said that Israel ''would leave all Lebanon'' if the Lebanese Army proved it ''could control the evacuated areas.''
This tallied with private analyses by well-informed Israelis that Israel might eventually leave south Lebanon if adequate security arrangements could be made to protect northern Israeli towns, even if Syrian troops remained in Lebanon. But Mr. Arens specified that Israel would not leave Lebanon's Bekaa Valley until the Syrians and the PLO pull out their troops.
The Israeli pullback in Lebanon has put an official end to Israel's one-time hope that it could impose a ''new order'' in Lebanon marked by predominance of the Christian Maronite sect and a strong central Lebanese government. This hope ran up against the reality of the need for Christian political compromises with Lebanon's Muslim majority.
Israel had hoped to pull all its troops out under the terms of the Israel-Lebanon accord of May 17, 1983. But the accord was contingent on a parallel pullback of around 40,000 Syrians and 10,000 PLO troops. They have refused to go.
Israel could withdraw unilaterally, but hasn't, both for security reasons and because of the high domestic political cost of such an about-face. The pullback is a compromise, easing public unhappiness over the protracted Israeli stay in Lebanon while shortening lines, cutting man power needs and hopefully lowering casualties.
It is also aimed at getting Israel out of the cross fire between the druse and their historic arch-enemies, the Maronites, whose phalangist militia Israel had allowed into the Druse-controlled Shouf in the long ago days when it still hoped the Maronites could dominate Lebanon.
In a stunning role reversal, Israel had recently showed increasing sympathy for the overall Druze position, not only because Israeli Druze play an important role in the Israeli Army, but because it was disillusioned with its Christian Phalangist allies and judged the Druse to be the potential victors in the Shouf. Israel also preferred to see the Druze politically satisfied rather than, as has happened, have them turn to Syria for support against the Christians.
Israel tried to mediate a political agreement between the Druze and the Lebanese government that would have permitted the Lebanese Army to take over Israeli positions. Mr. Arens blamed the failure of these efforts, in which the United States was also deeply involved, on lack of resolve by the Lebanese government to reach a political accommodation with the Druze. ''The Lebanese government . . . didn't seem to have the political will . . . to do what needed to be done,'' Mr. Arens said.
When these efforts failed, Israel rejected US pleas that it remain in the Shouf. Despite their intimate involvement with all the actors, Israeli officials are taking pains to deny any responsibility for the current bloodshed in the Shouf.