A Katyusha rocket plowed into northern Galilee last week. Israel's ''Peace for Galilee'' operation was supposed to put an end to that.
So far it hasn't, and it doesn't appear that it will for at least several months, according to both the Palestine Liberation Organization (PLO) and Western diplomats. Nor will Palestinian hit-and-run attacks behind Israeli lines stop. The same sources predict they will actually multiply.
''The Israelis are in the Lebanese quagmire sinking fast. They are up to their shoulders not knowing which way to look,'' said a Western diplomat.
The respected independent Lebanese newspaper, al-Nahar, estimated that despite its overwhelming superiority, Israel has knocked out only about 40 percent of the PLO's military apparatus.
Even when the PLO was full strength - roughly 20,000 men before the invasion - it was no match for Israel. Western diplomats believe there are now about 100, 000 Israeli soldiers in Lebanon - not to mention their modern tanks and artillery and sophisticated intelligence.
''Despite the fact that they are badly equipped and badly outnumbered, the Palestinians have done surprisingly well,'' said one Western diplomat.
''They have old tanks which are useless, multiple rocket launchers, and rocket-propelled grenades. When it comes down to it, house-to-house fighting will be the only tactic,'' he said.
Israel is talking about getting the 6,000 to 8,000 guerrillas out of Lebanon. But a cross-section of sources put that figure closer to 9,000, including Syrian troops trapped in the capital.
One Western military attache predicted that half this number would ditch their fatigues and Soviet AK 47 assault rifles if the Israelis came into west Beirut after several days of saturation bombing and shelling.
The four straight days of bombing attacks on Beirut as of July 25 had not prompted such a fading into the woodwork yet.
''You have to remember what happens to people caught by the Israelis with guns in their hands,'' a diplomat said.
''But many including Lebanese would still have a gun at home and wouldn't miss their chance to pick off an Israeli patroling a darkened Beirut street corner even months after the Israelis took west Beirut,'' he added. ''Occupation armies are never popular.''
Diplomats and PLO officials said this is what is happening in southern Lebanon. The PLO last week began issuing daily reports of behind-the-lines ambushes in southern Lebanon and the Bekaa Valley.
Israel said its daily air strikes were retaliation for these attacks. The PLO estimates its commandos have killed or wounded about 100 Israelis in these attacks - including senior officers.
''Every Israeli soldier around Beirut is now wearing bullet-proof vests,'' said an aide to PLO chairman Yasser Arafat. ''We are carrying out about four operations a day behind the lines,'' he said. ''We are not fighting like a classical army. We are not fighting for territory. We are out to bug them by hitting their Achilles' heel - casualties,'' the aide said.
''They are responding by hitting our Achilles' heel - using Uncle Sam's planes.''
The aide said the PLO was still in direct contact with its guerrillas roaming free in southern Lebanon. His only answer to how many there, was ''lots.''
''Every day there are more successful operations it encourages others to join , even Lebanese. The Lebanese are now cooperating more and more in the south by hiding guerrillas and feeding them. The Israelis will have to line up whole villages or put an Israeli soldier in every home to stop this,'' the PLO official said.
Last week Israel imposed a curfew in the southern port of Sidon after several ambushes.
Western diplomats agreed wholeheartedly with the PLO official.
The diplomats said Israel was playing on local alliances in the south and that will backfire on them. The Israelis have turned over much of the south to Maj. Saad Haddad, the Christian Lebanese Army officer who has long been collaborating with Israel.
Before the invasion Major Haddad controlled a wide border strip with Israeli help and imposed his own government and military which was anti-PLO.
Now he is reimposing his rule over a much larger section where the population is predominantly Shiite. Already there are incidents signaling brewing rebellion.
''Israel has given us the ideal situation for guerrilla warfare. These ambushes are being executed by men who know the local terrain well,'' Mr. Arafat's aide said.
Both the guerrillas in the south and in Beirut are well-stocked with ammunition, according to the PLO and diplomats.
''Even if we weren't, some factions in Lebanon who are supposedly anti-PLO have offered to sell us weapons,'' a PLO official said.
Western diplomats said the Israelis could take west Beirut in a matter of hours with minimal losses. Holding it would cost them, they said.
Most of the Palestinian weapons are highly mobile.
Most of their antiaircraft guns, Katyusha rocket launchers, and artillery are mounted on jeeps that are on the move through west Beirut day and night.
The guerrillas often fire a hail of rockets and then move to an entirely different neighborhood before the Israelis pinpoint them.
Arafat's own militia group, Fatah, was ordered not to move their heavy guns into the heart of Lebanese west Beirut.
Fatah officials say the reason was three-fold. Fatah wants to avoid Israeli reprisals on densely populated neighborhoods. Secondly, it wants to make it crystal clear that Israel hits civilian targets where there are no guns. Lastly, Fatah wants to avoid turning the Lebanese against the Palestinians.
Arafat demands two lists at the end of each day. One details casualties - both civilian and guerrilla. The other is an inventory of weapons and their positions, sources close to Fatah said.
''Expect many rockets to hit Galilee. Then don't be surprised if the Israelis start asking why their sons died without fulfilling 'Operation Peace for Galilee.' ''