Serious clashes between Lebanese right-wing militias and United Nations peacekeeping forces are inevitable if the U.N. commander goes ahead with his announced intention to extend the Lebanese Army presence in the southern part of that country, the Israeli Army command warned today.

A 500-man battalion of Lebanese regulars already has established positions dangerously close to the Israeli-backed secessionist enclave that runs along Israel's northern border, a senior Israeli Army official said, and another battalion is expected in the area within a day or two.

The senior officer, who under Israeli Army rules cannot be identified, accused Maj. Gen. William Callaghan, commander of the U.N. Interim Forces in Lebanon, or UNIFIL, of attempting to alter the balance of power in southern Lebanon. This would make it easier for Palestine Liberation Organization guerrillas to infiltrate into Israel for terrorist strikes, he added.

"If Callaghan continues to try to change the area, there definitely will be clashes -- there is no doubt about it," the Israeli official said in briefing foreign correspondents before a tour of the southern Lebanese enclave.

His warning followed an Israeli Army raid on the Lebanese village of Touline, about six miles across the border, in which, according to the Israeli Army, four houses were blown up by Israeli commandos. The Army command said one of the houses had been occupied by a PLO scout who assisted in last April's terrorist attack on an Israeli border kibbutz at Misgav Am in which two civilians were killed.

A UNIFIL spokesman in Beirut said the Israeli commandos exchanged small arms fire during the attack with a mixed patrol of Nigerian UNIFIL troops and Lebanese Army regulars deployed in the village. One Lebanese soldier was killed trying to dismantle an explosive charge planted on one of the houses and another was wounded, villagers told reporters who went to Touline, in the first reported clash between Israeli and Lebanese regulars since the latter were deployed in the south.

The Israeli command acknowledged that one of its soldiers was wounded in the raid, but denied that there was an exchange of fire with the Lebanese regular troops and the Nigerian UNIFIL troops as reported by villagers and UNIFIL spokesman Samir Sanbar in Beirut.

The Israeli version was that the commando was wounded by gunfire from villagers as the Israeli unit withdrew from Touline.

Maj. Saad Haddad, commander of the enclave's militias, said in a news conference here that Callaghan is to blame for the increased tension for allowing Lebanese troops to establish positions close to the enclave. He warned that his militias will engage the UNIFIL forces if Lebanese regulars continue to move south.

A U.N. spokesman in New York said about 600 Lebanese soldiers have been attached to UNIFIL forces in the area for the last two years and that to his knowledge their numbers are not scheduled to grow.

[Washington Post special correspondent Nora Boustany in Beirut noted that Callaghan has made a number of statements since he took over last month emphasizing his determination to carry out with more vigor than in the past U. N. Security Council Resolution 425 of March 19, 1978. That resolution ordered UNIFIL's creation and mandated it to restore Lebanese government authority in the entire southern Lebanese area, including Haddad's enclave, following an invasion by Israel against Palestinian guerrilla concentrations there.]

While expressing doubts that the U.N. forces will fight even if ordered by Callaghan, Haddad declared, "If they follow his orders, we are ready to fight. He is pushing us to fight. They are not our enemy -- the PLO is our enemy -- but the red line for us is the [enclave] border. They cannot approach our border."

Two weeks ago, following the deaths of three Nigerian UNIFIL soldiers in an artillery attack by Haddad's forces on the town of Kantara north of the enclave, Callaghan said he intended to fulfill the U.N. mandate by installing the Lebanese Army there even if it means UNIFIL casualties.

Throughout today's five-hour tour of Haddad's enclave by the Israeli Army command, Israeli officials sought to portray the UNIFIL forces as inept and sympathetic to Palistian guerrillas in their area.

One liaison officer, pointing to a Nigerian checkpoint, said that when PLO guerrillas approach the checkpoint, they are given cursory examination by Nigerian troops who do not speak Arabic, Hebrew or English. "All they ask is, 'You have boom-boom?'" the Israeli officer said. "If the answer is no, they let them go."

When correspondents approached the checkpoint and asked a Nigerian soldier on duty if he spoke English, he answered in crisp British accent: "We're from a former British colony. Of course we speak English."

The Israeli-UNIFIL dispute has escalated steadily late last month, when Callaghan had an introductory meeting with the Israeli northern commander, Maj. Gen. Avigdor Ben-Gal, following the Nigerians' deaths.

Immediately after the meeting, the Israeli Army command issued a statement saying Callaghan had "demanded" complete freedom of movement of his troops in all southern Lebanon, an end to Israeli Army presence in the area and an end to Israeli assistance to Haddad's militias.

Describing the meeting as being conducted in a "tense atmosphere," the Israeli statement said that "changing the status quo" in southern Lebanon would endanger Israel's security and that Callaghan had appeared "unsympathetic" to that concern.

Later, the United Nations denied that Callaghan had demanded anything in the meeting, but said he had simply "requested" Israeli assistance in permitting the UNIFIL forces to fulfill their mandate. The United Nations said Callaghan also requested "the cessation of movement" of Israeli troops along certain roads in southern Lebanon.