By such unusual devices as hot-air-balloons, hang gliders, and speedboats, Palestinian guerrillas -- terrorists in Israel's terminology -- have been and probably will go on trying to penetrate the Jewish state's nearly hermetic borders on missions of death and destruction.
The latest instance, April 16, involved two balloonists shot down near Kibbutz Menara on the Israel-Lebanon frontier. They are killed in a brief ground skirmish.
Military spokesmen reported that the pair of Palestinians were equipped with weapons and sabotage equipment intended for use in a prolonged hostage-taking episode. If they had succeeded, the lives of Israel civilian captives presumably would have been offered in exchange for Palestinian comrades in Israeli prisons.
Resort to unconventional methods of border penetration evidently stems from two current realities of the unending Palestinian-Israeli dispute:
1. The Palestinian's determination to carry out attacks inside Israel regardless of the obstacles put up by Israel's security system.
2. The Israelis' relentless military pressure against Palestinian bases along Lebanon's Mediterranean seacoast and inside the area patrolled by the United Nations Interim Force in Lebanon.
In fact, the abortive attempt to enter by balloon was followed within less than 12 hours by an Israeli Air Force strike against a Palestinian base said to be situated at Ras-al-Ein, near the ancient Phoenician port of Tyre.
All the aircraft returned safely to base after scoring "accurate hits," a communique said.
The unconventional approach to the problem of entering Israel was first demonstrated March 7 when two armed Palestinians flew across the Lebanon-Israel border by hang glider, touched down in nearby sites in Galilee, and were promptly intercepted by troops and police.
After vanishing into Israel's top-secret guerrilla-terrorist detention centers, the two were produced for local reporters to announce that they were trained in hang glider flights by Syrian instructors in Syria.
Deputy defense Minister Mordechai Zippori reacted instantly to the balloon incursion by announcing that this mission was also staged in collusion with the Syrians. The balloon itself was of British manufacture, a military spokesman said.
The use of speedboats and other small seagoing craft harks back nearly a decade when the difficulties in crossing overland prompted Palestine Liberation Organization (PLO) tacticians to try to take advantage of Israel's long coastline.
This usually meant the use of a mother ship, such as innocent-looking freighter or fishing boat from which the small craft with their squad-size crew were dropped into the Mediterranean off the coastal target.
One of these missions resulted in the death of a father and small daughter and another in the seizure and eventual destruction of Tel Aviv's delapidated Savoy Hotel, in which guests and staff were held hostage for nearly 10 hours until it was stormed by crack antiterrorist troops.
Israel's problem in trying to foil unexpected, if not ingenious bids, to penetrate the frontier stems partly from its own technological success on the ground.
During the past decade, electronic security fences were stretched along the whole length of the border and cease-fire lines between Israel, Lebanon, Syria, and Jordan.
These are backed up by mine fields, searchlights, mobile patrols, and other secret techniques intended to make it almost impossible for would-be infiltrators to get through.
However, an outfit like the PLO, whose ideology includes a call for constant struggle against Israel, cannot be expected to concede to technology or military methods.
The fact that a meeting of the Palestine National Council has been under way in Damascus, Syria, may well have given an added impetus to the PLO's determination to fight on, if only to demonstrate to the moderate wing that militant elements will not lay down their arms.
For their part, Israeli military commanders repeatedly stress that the public cannot expect the country to be sealed like a vacuum jar -- and thus must always allow for the possi bility of a successful penetration.