Israeli forces, in their biggest military assault in southern Lebanon since the summer of 1982, today stormed a town north of their current front line, overwhelmed a defending Lebanese Army unit and killed at least 34 Arabs that an Israeli spokesman said were suspected Shiite Moslem guerrillas.

The attack on Zrariyeh came a day after 12 Israeli soldiers were killed in a suicide truck-bomb attack near the Israeli border. An Israeli Army spokesman denied that today's raid was in retaliation, but reporters who went to the scene after the Israelis had withdrawn said they saw newly painted slogans claiming "This is the revenge of the Israeli Defense Forces."

An Israeli military official in Tel Aviv said late tonight that 34 Lebanese had been killed and seven wounded and that there were no Israeli casualties, Washington Post correspondent Edward Walsh reported.

Figures compiled from Lebanese security, military and hospital officials put the death toll at 30 or more, with many others wounded and at least 100 captured, including the Lebanese soldiers. Israeli troops blew up at least 11 houses where they reportedly found large supplies of weapons.

Zrariyeh, a town of 10,000 people, is about three miles north of the Litani River, the northern boundary of Israel's current occupation zone. As the first phase of its planned three-phase withdrawal from Lebanon, Israel last month pulled its troops from the Awwali River north of Sidon to the Litani, just north of Tyre. But it has continued to raid villages north of the Litani in an effort to halt attacks on its troops by Shiite Moslem guerrillas.

Reporters and rescue workers, barred from the area by Israeli soldiers during the attack, reached the village late today and told of finding scorched bodies scattered on the side of the approaching road. Six destroyed autos were seen with bodies inside, the reporters said.

Associated Press correspondent Samir Gattas said he counted at least 12 bullet-riddled bodies lying beside cars, and he said that the track of an armored personnel carrier could be seen on the rooftop of a crushed automobile that had a man's body sandwiched inside. A photographer for Reuter said another body lay crushed underneath the car.

An Israeli military official told Walsh that the death toll was far higher than in previous raids against villages suspected of harboring anti-Israeli guerrillas because "apparently a number of them resisted. This was a large terrorist base and the attack came as a surprise."

"There was considerable fighting," he said, "and many of them tried to escape in vehicles that were loaded with arms and explosives." He said the Israelis found "huge quantities" of weapons and explosives in the village.

The highest previous toll since the 1982 invasion and its immediate aftermath was 11 suspected guerrilla infiltrators killed near the Awwali River last month.

Israel Army Radio reported that during today's operation Israeli forces also shelled three other nearby Shiite villages.

Nabih Berri, Lebanon's Cabinet minister for southern Lebanon and leader of the Shiite Amal movement, condemned the "massacre" and Aly Hamdan, of the Amal information section, called it "a collective Israeli slaughter of innocent civilians." A senior Amal official, however, said the Shiite organization had lost 17 of its men in the battle. "I know most of them; they must have fought down to the last bullet they had," he said, after hearing some of the names.

The Israeli assault, preceded by several hours of heavy shelling, used helicopters and tanks, witnesses said, and led to daylong combat involving armor, rockets and hand-to-hand fighting before the Israelis withdrew about 5 p.m.

Hamdan said 110 Israeli armored vehicles rumbled into Zrariyeh at dawn from Ansar, three miles to the north, and from Arzay to the west.

A unit of 30 Lebanese Army soldiers stationed at Zrariyeh, the closest Lebanese Army post to the current Israeli line, opened fire but failed to block the Israeli push.

An Israeli military official said in Tel Aviv that 20 of the Lebanese soldiers had been taken into custody by the Israeli forces but that they would be released after interrogation. All the Lebanese soldiers in Zrariyeh were Shiites, the Israeli said, and "could be expected" to fight alongside their fellow Shiites.

"The operation in the village was carried out in the wake of attacks from this sector, as well as of reports on preparations for terrorist activities against our troops," an official Israeli statement said. "The Lebanese Army was told not to interfere with the IDF Israel Defense Forces action, and only after they fired at our troops were they fired upon and 20 of their soldiers detained."

"We stood our positions as long as we could, then they took our weapons, uniforms and military papers," one soldier told The Associated Press. Lebanese military sources said there were at least six casualties among the soldiers.

Military sources here said Army reinforcements were sent toward the town, but radio contact was lost between Lebanese Army headquarters and Zrariyeh at midmorning. The modestly equipped Lebanese Army unit would have been unable to match the firepower of the Israelis, they said.

During the assault, Israeli troops fired a tank shell into a group of approaching Lebanese Red Cross workers and correspondents, sending them diving for cover, witnesses said. Two Red Cross vehicles waiting at villages close by were warned by radio by the Israelis not to advance into Zrariyeh.

Film reaching Beirut tonight showed scenes of panic among fleeing villagers, with anguished women looking for relatives and cars wrecked by shells on roads leading from Zrariyeh.