KAFRA, Lebanon (AP) _ Arab guerrillas fired rockets into Israeli-held territory today, and Israeli artillery hit southern Lebanon, forcing thousands of Shiite Muslims to flee their villages.

Israeli also struck from the air, sending its jets to attack bases of the Shiite Muslim Hezbollah militia in south Lebanon, the Israeli military command said. It was Israel's fifth air raid in Lebanon since Sunday.

Following the guerrilla rocket attacks, 13 Israelis were treated at a clinic in the northern Israeli town of Kiryat Shemona. Israel radio said most of them suffered shock and two required hospitalization.

For three straight days now, rocket and artillery attacks have occurred on both sides of the Israel-Lebanese border. The violence began after Israel assassinated Sheik Abbas Musawi, leader of the pro-Iranian Hezbollah, in a helicopter raid in south Lebanon on Sunday.

The guerrillas' Soviet-designed Katyusha rockets landed in Israel's self- proclaimed security zone in south Lebanon and in northern Israel, the Israeli army said, but it refused to give exact locations.

Israel's howitzer, mortar and tank fire forced most of the people in the Shiite villages to flee, but no injuries were immediately reported.

Four rounds per minute rained down on the Shiite villages of Kafra, nearby Yater, and the hilltop hamlet of Kabrikha.

Mohammed Kawtharani, 57, and his wife, Fatima, loaded household goods in their car and left Kafra for the nearby town of Qana, beyond the firing range.

''Only God knows what will happen here. The Israelis could do anything,'' Mrs. Kawtharani said. She said tearfully that they would stay with friends in Qana ''until this ordeal is over.''

Howitzer shells exploded between the houses of the hamlet as a school bus driver asked a U.N. peacekeeper if he could drive a pupil to her home in Kabrikha. ''What home?'' the Irish soldier replied angrily. ''You'd better get the hell out of here as fast as you can. It is getting nasty.''

A security source said Israeli and allied gunners of the South Lebanon Army militia fired 400 howitzer, mortar and tank cannon rounds at Shiite villages bordering the security zone overnight in addition to hundreds of parachute flares that illuminated the whole region.

Lebanese radio stations said Israel moved 40 tanks, 60 armored personnel carriers and 12 howitzers into the security zone overnight. But police and reporters in the security zone could not verify the buildup.

In the air attack, the Israeli jets struck Hezbollah militia bases in the town of Jibsheet, nine miles northwest of Israel's panhandle, according to a military statement issued in Jerusalem.

The statement said ''the target was hit and all planes returned safely.''

Lebanese police said no casualties resulted because guerrillas had abandoned the targeted buildings due to the recent upsurge of violence.