Already caught up in deliberations over how to respond to the recent movement of Syrian surface-to-air missiles into Lebanon and last weekend's terrorist attacks against El Al Israel Airlines at the airports in Rome and Vienna, Israeli leaders today faced a new military challenge on their northern border.

Five Katyusha rockets fired from Lebanon landed in northern Israel early this morning, sending the residents of the country's largest border town, Qiryat Shemona, hurrying into bomb shelters.

While Israeli military sources said that there were no casualities in the attacks, a rocket that landed in the centerr of town damaged four cars and shattered nearby apartment windows.

Prime Minister Shimon Peres told reporters that Israel would take the necessary steps to halt the politically volatile rocket attacks, but he said it would be difficult to pinpoint those responsible "because there are so many forces acting in an uncoordinated manner" in Lebanon.

(Israeli troops and the Israeli-allied South Lebanon Army (SLA) militia shelled targets in southern Lebanon later today in retaliation for the rocket attacks, Reuter reported.

("We shelled areas from Jazzin to Naqoura in which there was guerilla activity and we will fire in the future on areas from which we are fired upon," said Antoine Lahad, the SLA commander. An Israeli military source said Israeli Army gunners also fired artillery.)

Northern District Army commander Maj. gen. Ori Orr said in an interview on Army radio that "if we find out that this is the beginning of a new process, we will react, and not only the residents of Qiryat Shemona will remain sleepless."

His comments were seen as a warning that Israel would unleash artillery or some other form of military response against any guerrilla targets it can identify in southern Lebanon. However, another defense source said that it would be a few days before it is clear whether the attacks were an isolated incident.

Officials also said that Iranian-backed Hezbollah guerrillas are now opearting in southern Lebanon. U.N. peace-keeping troops have reported seeing Iranian flags openly exhibitied in the area, although such flags previously were banned by Amal, a less radical Shiite Moslem militia.

It was ostensibly to end frequent rocket attacks against Qiryat Shemona, which has a population of 10,000, and other northern settlements that Israel invaded Lebanon in 1982. The action, known here as "Operation Peace for Galilee," successfully smashed the Palestine Liberation Organization's infrastructure in the south.

But, as the incursion evolved into a three-year military occupation, it turned the local, mostly Shiite Moslem population against Israel. Israel still has several hundred troops stationed in a six-mile-deep "security zone" it has declared in southern Lebanon, and it supports the SLA, a mostly Christian militia that is supposed to help prevent attacks on Israel's northern border settlements.

Yesterday, Israeli troops patrolling in the security zone killed one Lebanese guerrilla and routed others who were getting ready to launch a rocket attack, the military command said.

That night, the SlA began shelling Yatar and other Shiite villages north of the zone, according to Timor Goksel, spokesman for U.N. peace-keeping forces in the region. Israeli radio reported today that the SLA shelling was continuing.

The rocket attacks came just hours after Israel's so-called "inner cabinet" of senior government ministers discussed ways of dealing with last week's Rome and Vienna airport assaults and the latest Syrian missile crisis.

"Now we have another dimension," commented one Israeli government official.

Three surving terrorists have told investigators that they represent a Palestinian splinter group headed by terrorist Sabri Banna, known as Abu Nidal, who broke with the mainline PLO a decade ago. Peres said in a report to the Israeli parliament yesterday that the group's "main strength today lies in Libya," although it has also received support from Syria and Iran.

The Syrian missile crisis has been brewing for about six weeks, with Israel contending that the repositioned weapons change the status quo in Lebanon and threaten Israel's vital "freedom of the skies" in the areaa reference to Israel's insistence on a right to conduct aerial surveillance over Lebanon. Israel wiped out Syrian surface-to-air missile batteries in Lebanon in the first days of its 1982 invasion of Lebanon.

The Israeli official refused to say whether the ministers approved any specific actions at their Cabinet meeting yesterday, although he did comment: "We will not let terrorist activities, whoever carried them out, go unanswered. They will be answered."

Like other sources in the last few days, however, this official appeared anxious to discourage speculation about some imminent military response to either the airport attacks or the Syrian missiles.

"As long as people are nervous, that's good enough for us for the time being," the official said.

Israelis have lived before with Syrian missiles in Lebanon's Bekaa Valley, noted a senior defense source, referring to the period between the spring of 1981, when such weapons were first deployed there, and the June 1982 Israeli attack that wiped them out. "We have a lot of time," he said. " ou have to wait for an opportunity and an occasion to do it."

The sources said that Israel could easily knock out the Syrian missiles, but that the government is concerned that this might cause a wider conflict that neither Syria nor Israel really wants right now.

While Peres has harshly critized Libya as a "murder state" in connection with the airport attacks, Israel also appears less inclined to retaliate quickly for those actions than it did in the first hours after them.

"There are some who propose a military action against Libya," Peres told the parliament yesterday. "However, before one speaks of military operations, some simple questions have to be asked: Why is Libya treated with a measure of forgiveness and a closing of eyes" by much of the international community?

Even though the airport attacks were directed against El Al check-in counters, most of the casualties were non-Israelis, and officials here clearly feel that the burden of responding should not be left to them alone.

"they don't want the burden of being the spear-carrier for antiterrorism," said one source close to the government.