Beirut — The vise is tightening on Lebanon.
From the cafes and boutiques along Ras Beirut's bustling Hamra Street, one can look up and see Israeli jets careening over the city, puffs of antiaircraft smoke popping behind.
The booming of artillery could be heard from the south, near Damour, a Palestinian stronghold where heavy fighting was taking place June 8.
With the Israeli Army pushing relentlessly toward Beirut, the principal parties that have been vying for power in Lebanon are either suffering from the Israeli blitz and growing weaker, or husbanding strength for the power-struggle that is bound to follow.
The 600,000 Palestinians in Lebanon almost surely will end up the greatest losers on the battlefield. And depending on the blows the Israeli Army ultimately deals the Palestine Liberation Organization, the PLO might also be the political loser.
As the Israelis move northward, the Palestinians are pushed back toward territories controlled by the Lebanese Christian Phalangists to the north and the Syrians to the east. The PLO infrastructure is being pummeled by the Israeli military.
The Palestinians may either have to make a last stand in the Beirut area or submit to Syrian, Lebanese, or Phalangist domination. Either way, they could lose their independence for good.
Neighboring Syria, which has maintained a military presence in this country since 1976, also stands to lose a great deal because of this dilemma. As chief backer of the PLO, Syria must commit forces to at least a show of battle against Israel. But if Syria fights too hard, that could incur an Israeli retaliation that might threaten Syria's grip on Lebanon.
''Where are you, Syria?'' Syria's closest ally, Libya, asked over Tripoli radio June 7.
Due to such pressure, Syria is daily increasing its military commitment against Israel. On June 8, reports indicated Israeli jets had bombed the Syrian stronghold in Lebanon of Jezzine and downed six Syrian MIGs.
In the end, the cost of losing face could prove much less than the potential military cost to Syria of joining the war. A devastating Israeli retaliation could severely damage Syria itself and possibly topple the government of Hafez Assad.
The indigenous forces in Lebanon are playing a waiting game, watching the skies and the turning of events before making their move. Chief among these groups are the Phalange (mainly Maronite Christians) of East Beirut, the ''Amal'' Shiites of West Beirut and southern Lebanon, and the Druze of the central Shouf region.
The Phalange is making no hasty military moves, despite urging by the Israeli-backed Maronite leader, Saad Haddad, in southern Lebanon to join the fight. Instead, the Phalange is calling vaguely for a postwar dialogue among native Lebanese to reestablish the state of Lebanon.
These parties, a Phalangist official said, would include the Phalangists, the Shiites, the Druze, and the Sunni groups in Lebanon -- but not the Palestinians or the Syrians.
''The Syrians must leave,'' the Phalangist said. ''And the Palestinians must disarm and submit to Lebanese authority.''
But the Phalange would not force the issue, he said.
''It would be suicide for us'' to confront the Syrians and the PLO, the official said. ''We must wait for events to sort themselves out. Then we would not mind going in to reestablish Lebanese authority at the invitation of the government.''
If the Phalange is the most well-organized and well-financed native force in Lebanon, the Shiites are the poorest and have the most potential in the post-invasion Lebanon, Lebanese analysts agree.
The Shia constitute some 950,000. They are the largest single minority in Lebanon. Their heartland is southern Lebanon, which for the past six years has been under increasing Palestinian and Syrian influence.
The Shia have frequently fought the Palestinians. But they have fought the Israelis just as often.
The leader of the largest, best organized Shia group, the ''Amal'' party, has conferred with PLO leader Yasser Arafat and Syrian Foreign Minister Abdel Halim Khaddam frequently during the invasion.
Outwardly Amal supports the Palestinians. But the group is known to have sub rosa links with the Phalangists. And the area controlled by Lebanese Maj. Saad Haddad has both Shia and Maronite residents, who - backed by the Israelis - have formed the fighting force in ''Haddadland.''
Even more of a riddle are the Druze, who occupy the central Lebanon mountains where much of the fighting was occuring June 8. Druze leader Walid Jumblatt is allied with the Syrians and the Palestinians even more than Amal. But the Druze, like so many groups in this chameleon country, have proven historically to be loyal to whatever power is the strongest.
Iraeli Arabists have characterized the Lebanese Druze as being much like the Druze of the Israeli-occupied Golan Heights, many of whom serve in the Israeli Army.
But by the third day of the Israeli invasion, the changing situation on the ground was still unclear. And the Lebanese were watching and waiting, standing on the streets with heads cocked skyward, as the Palestinians and the Syrians wrestled with the invaders.