Just two weeks after Israel invaded southern Lebanon in retaliation for a Palestinian terror raid, a public debate is raging in Israel over whether the massive operation has been worthwhile.

Spurred by increasingly probing and critical articles by Israel's much respected military commentators, the Defense Ministry has sought to justify various aspect of the operation.

Politically, there is an increasing public awareness of divergencies in government ranks symbolized by Foreign Minister Moshe Dayan's tightlipped refusal even to mention the invasion.

The whole operation is now generally seen as the brainchild of Prime Minister Menachem Begin and Defense Minister Ezer Weizman.

A common theme of much of the criticism is that the Israeli invasion failed largely because - as with the Americans in Vietnam - there was too much reliance on firepower to cut casualities.

"Soldiers are returning embittered over what the Lebanese underwent as a by-product of the Israeli operation, which caused more suffering to civilians than to the intended target," the Palestinian guerrillas, Teddy Preuss wrote in Davar, a newspaper close to the opposition Labor Party.

Another Israeli commentator spoke ironically of "the effect of saturation bombing on Israeli troops" unaccustomed to such massive destruction caused by naval, artillery and air bombardment.

Israelis are coming to realize that Palestinian commando morale is higher than in many years.

Continuing Guerrilla rocket and artillery fire against northern Israel has also underlined the emptiness of initial Israeli claims that the invasion was designed to establish a six-mile-deep security belt in southern Lebanon to stop such terrorism.

Increasingly Israelis are realizing that a double Israeli fence, electronics equipment and constant patrolling in recent years had all but ended direct cross-border guerrilla raids.

Israeli critics have also pointed out the armed force's tactical errors. Basically the Israelis had never fought this kind of war before - and their performance showed it.

They had no forward air controllers in light observation planes to pinpoint targets. As a result, reliance on high performance jets - including the F15 made precise targeting impossible and may have led to overly massive and unneeded artillery and air strikes.

Another common theme in the press is the fear that a prolonged presence in southern Lebanon could degenerate into another war of attrition of the kind that cost Israel hundreds of casualties along the Suez Canal in 1969 and 1970.

The invasion also formed Israeli attention on the less savory side of its policy of cooperating with the Christian militia along the Lebanese border.

One military commentator wrote that the Christian allies "didn't show themselves to be an effective military force, but did turn out to be good at massacres."

Television news has shown signs of Christian militiamen looting homes of their Shiite Moslem neighbors.

"You could practically feel the vibrations around this country," a psychologist remarked, "at the sight of looted goods being piled into Christians' cars and trucks.

Increased questioning of the Christians' role, once taken for granted, was manifest in yesterday's Jerusalem Post. It reported that Moslems had no intention of joining in the so-called southern Lebanese army, a mix of Christians and Shlite Moslems, set up by Maj. Saad Haddad.

Summing up the current of criticism, Preuss wrote "We are stuck" and "the real question is how to get out.

"Israel's commitment could well lead a Vietnam-like problem for us: angry and divided public opinion, a heavier security burden, greater hostility internationally.

"Nor would Isreal be strong enough to withstand all this and not even the prime minister's resignation would be enough to preclude a major disaster."

Zeev Schiff, the recognized dean of military commentators, wrote in Haaretz that the Poltical thinking "from the beginning was defective and confused and did not foresee events where the most elementary things were concerned."

Symptomatic of the confusion, he said, was that "suddenly there is a strange desire for the United Nations to succeed in its task" in Lebanon or for the Syrians to muzzle the guerrillas down to the Litani River.

Never before have the United Nations or Syria been in such good Israeli graces.