Incidents of fighting between Shiite Moslem militiamen and the Israeli-backed South Lebanon Army are escalating, according to Lebanese security sources and U.N. peace-keeping officials.

A series of artillery exchanges peaked late Sunday night and early Monday with a combined barrage of SLA and Israeli Army heavy artillery and tank cannon against at least six Lebanese villages just north of the narrow security zone that Israel maintains above its border.

The barrage, which security sources here said was the worst since Israel withdrew most of its troops in June, included 40 tank cannon rounds fired from three SLA positions and four rounds of 155-mm artillery fired from an Israeli Army battery inside Israel.

The main targets were the villages of Buyut Sayid, Mansuri, Henniyeh, Ras el Ain, Majdal Zoun and an area near the Palestinian refugee camp at Rashidiyeh. Security officials and Shiite militia leaders said there have been no reports of casualties.

The shelling of villages controlled by the Shiite militia, Amal, followed a series of attacks with mortars, Katuysha rockets and machine guns against the villages of Yatar, Tair Harfa and Jibbayn in the security zone from positions north of the SLA-controlled strip.

So far this month, there have been more than 70 attacks against the Israeli Army and the SLA in the security zone, with the nightly average currently rising to four or five, security sources here said.

Timur Goksel, spokesman for the U.N. Interim Force in Lebanon (UNIFIL), confirmed the increase in attacks, saying, "All sides have been warned that we are going to have another cycle of violence in the area. It is totally predictable."

Amal militiamen, Goksel noted, have been under increasing pressure from splinter Shiite groups and Syrian-backed militias to escalate their attacks against the SLA from north of the security zone.

The accounts of escalating violence contrasted sharply with assessments offered in the last few days by senior Israeli military officials in a series of briefings that portrayed southern Lebanon as pacified and experiencing unprecedented cooperation between the local population and the SLA.

In what appeared to be a concerted media campaign, the Israeli Army Command maintained that a vast majority of the 220,000 residents of the security zone have accepted the presence of the SLA, resulting in improved intelligence forewarning against guerrilla attacks.

The Army also reported in the Israeli press that leaders of several villages outside the security zone had requested that their villages be included under SLA protection, and that the economy in the zone is prospering more than ever.

Israeli military sources estimate that the SLA militia commanded by Gen. Antoine Lahad numbers nearly 2,000 regulars, plus part-time civil guards in villages. Amal officials said the total was closer to 1,000, and claimed that defections from the SLA to Amal are increasing.

Amal has maintained consistently that it has tried to prevent attacks against Israeli troops and SLA militiamen from outside the zone to avoid reprisal attacks by the Israeli Army or providing the Israelis with a pretext for reoccupying a larger part of southern Lebanon.

Security sources here said that such groups as the Syrian National Socialist Party, Hezbollah (Party of God) and several other radical Shiite militias have stepped up a propaganda campaign against Amal, branding the mainstream Shiite militia as "sandbags for Israel" because of its efforts to restrict attacks to indigenous operations against the Israeli Army and the SLA inside the security zone.

The head of Amal in southern Lebanon, Daoud Daoud, said in an interview in his heavily guarded home near here that the militia's basic policy still is to restrict attacks from outside the security zone to prevent harsh Israeli reprisals against Lebanese villages north of the zone.

But, Daoud said, an escalation of fighting was inevitable because of the increasing effectiveness of Amal operations and attacks initiated by other Lebanese militias.

In addition to daily artillery and small arms fire against SLA positions, 13 car bombs and two bombs attached to donkeys have been detonated at or near SLA checkpoints, most of them attributed to radical Shiite splinter groups or the Syrian National Socialist Party.

Referring to the step-up in SLA shelling of Lebanese villages north of the security zone, Daoud said, "All these actions mean that the resistance is effective. If we weren't effective, these procedures would not be taken."

Abdel Majid Saleh, an Amal political officer at the militia's headquarters here, said, "The operations will not stop until the Israelis withdraw and allow UNIFIL to move to the border."

The 1978 U.N. Security Council mandate for UNIFIL calls for deployment of the peace-keeping forces to the international border, but Israel has refused to accede to repeated U.N. demands that it be permitted to redeploy.