The shot on a London street that wounded Israel's ambassador June 3 was only the tripwire that unleashed the Israeli invasion of Lebanon.
The real cause of Israel's invasion was not simple revenge; it was security and political calculations that will be put to the test only after Israel secures its military objectives.
Most Israelis, including Gen. Rafael Eitan, the chief of staff, see the purpose of the operation as removing the threat of Palestinian shelling from northern Israeli settlements whose residents have long learned to sleep with an ear cocked for the whine of incoming rockets.
There are some, however - including Defense Minister Ariel Sharon - who see the invasion also as a means of removing the Palestine Liberation Organization as a serious political factor .
Israel had been unhappy about the United States initiated cease-fire achieved last July along the Israeli-Lebanese border. The accord put an end to heavy artillery skirmishing with the PLO.
Politically, the cease-fire was an indirect recognition by Israel of the PLO, which the Israelis maintain is a terrorist organization. Militarily, the cease-fire did not inhibit the Palestinians from building up their artillery and Katyusha rocket strength across the border and continuing to hold Israeli settlements hostage to sudden and massive shelling.
Prime Minister Menachem Begin and Mr. Sharon found it grating that the PLO should be inviolate adjacent to Israel's border while feeling itself free to operate against Israeli targets in Israel and abroad.
Although the PLO did not fire across the Lebanese border, it became apparent in recent weeks that it would not take much provocation for Israel to move against the PLO in southern Lebanon. The attack on Ambassador Shlomo Argov following a series of other terrorist attacks was the signal.
The 25-mile pushback of the Palestinians cannot be implemented in the northeast sector of southern Lebanon without Israeli forces coming into direct confrontation with the Syrian Army stationed in the Bekaa Valley.
Israel has said it will not pursue the Palestinians into the Syrian-controlled zone, but Israeli officials have also said they would not abide shelling of northern settlements from that area.
It should become apparent within the next few days whether the Syrians are willing to restrain the Palestinians within their zone. If they are not, or if they seek out a direct confrontation with Israel, then the fighting of the past week will probably pale before the conflict that will erupt between the Israelis and the Syrians.
The two sides have already clashed in tank and artillery skirmishes and eight Syrian planes have been shot down.
If the PLO is eliminated as an armed force in southern Lebanon, the question is whether this will eliminate what Israel regards as the PLO's capacity for mischief. Prime Minister Begin said June 8 in the Knesset (parliament) that it was possible to stamp out terrorist groups, citing the elimination of the anarchists at the turn of the century. But most Israelis are resigned to renewed PLO activism, whether in Israel or against Israeli targets abroad.
The elimination of a direct threat from PLO artillery, however, is widely applauded, even by many Israelis who previously had been opposed to a military incursion into southern Lebanon.
The effects of this week's battle on the PLO's political status remain to be seen.
Mr. Sharon has attempted to crush PLO influence on the West Bank by developing an alternative Palestinian leadership willing to become involved in autonomy negotiations under the Camp David agreement. The PLO has rejected this concept of autonomy as a guise for the continuation of Israeli rule in the occupied territories.
Mr. Sharon evidently believed the blow being dealt the PLO in Lebanon will significantly reduce its image as champion of the Palestinian cause.
''Sharon believes that the existence of the PLO infrastructure in Lebanon inhibits any negotiation with the Arabs,'' writes a columnist in the Israeli daily newspaper, Haaretz. ''He sees the PLO as a political danger, not a military danger.''
Most Israelis are willing to settle for the elimination of the military danger on the northern border.