In Israel's vulnerable northern cities April 22, schoolchildren began serious bomb-shelter drills for the first time in nine months - one consequence of the Israeli air raids into Lebanon this week.
''We have no choice. We have to learn to live with this,'' Nessia Elan told her three school-age children following the April 21 Israeli air raids. ''We speak to them and tell them everything, and we try to take away their fear,'' she explained.
From Metulla, where Mrs. Elan lives and works, one can peer easily into the hazy green fields of southern Lebanon. Last summer some 800 Palestinian rockets whizzed across the border during two weeks of Israeli-Palestinian fighting, pounding the area and seriously disrupting normal activity. Metulla, Israel's northernmost city, is just across the Beaufort Castle gap through which Palestinian and Israeli forces come into direct confrontation.
A United Nations officer who crossed from southern Lebanon into Israel early April 22 reported there was no sign of abnormal Palestinian or Israeli activity. But there is much concern here and in Tel Aviv that the Israeli air raids will prompt a Palestinian response.
''I know that the time will arrrive,'' said bank manager Levy Mayer of Kiryat Shemona, a populous city just south of Metulla that suffered a punishing attack last summer. ''I checked the shelter today for our employees. At any moment we could be hit by a Katusha (Soviet field rocket).''
An Israeli lieutenant described the current situation as ''playing along a very delicate line.'' He said Israeli forces were not necessarily on war footing and added: ''It is very difficult to say if the PLO will retaliate, or if some other Palestinian group will. But if they do, the government will retaliate massively. The government can't back away.'' At least 25 Arabs were reported killed in the Israeli attack.
In Jerusalem, US envoy Walter J. Stoessel Jr., who met with Prime Minister Menachem Begin at midday April 22, said he was urging both sides not to allow the July 24, 1981, cease-fire to fall apart. For their part, Palestinians based in Lebanon issued a statement saying the cease-fire effectively had been abandoned and warning that reprisal would follow.
Residents of this hilly, fertile farming region just north of Lake Tiberias (the Sea of Galilee) have vivid memories of the disruption and damage suffered last summer. Following the fighting, some 200 families fled the city of Kiryat Shemona (population 13,000). Economists say the city's economy suffered heavily.
''If those PLO men begin again to shoot rockets, I expect my government to do something at once - to move them far away from our border,'' says Mr. Mayer. I think we have the right to live here without these kinds of risks. . . . I think it is very difficult for someone who does not live here to know how we feel.''
Reliable sources have reported that the Israeli Army is massed along the Lebanese border and that Palestinian forces are fairly distant - possibly as far north as the Damur stronghold just south of Beirut. UN and Israeli officers say they believe the Palestinians are reluctant to move their heavy equipment and fighters south of the Litani River, or even south of the Zaharini River, for fear they might be caught in an Israeli offensive.
Thus, the occupants of Thirea are waiting for the other shoe to fall. And in the places it will fall - the villages and houses of northern Israel - there is a certain resignation about going back into the bomb shelters.
''No, it's not nice to be sitting in the shelters in the dark for a week,'' says Mrs. Elan. ''It's not so easy, but we know it's part of life here.''