After months of talk of a "hot summer" with Syria and a long battle of attrition with Palestinian Kassam rocket launchers in Gaza, Israel finds itself facing the prospect of a major military escalation on two fronts.

In the North, Syria has warned that it will retaliate at a time of its choosing against the alleged Israeli penetration of its airspace on the night between Sept. 5 and 6.

In the South, Defense Minister Ehud Barak says a major Israeli ground offensive in the Gaza Strip is "only a matter of time."

Israeli officials refused to confirm or deny whether the alleged Israeli Air Force overflight of strategically sensitive areas in northern Syria actually took place. But if they hoped their silence would defuse the situation, they were mistaken. It seems the affair could lead to repercussions not only with Syria but with Israel's close ally Turkey, too.

A jettisoned fuel tank believed to be from an Israeli F-15 was found in Turkish territory near the border with Syria, and the Turks have asked for an explanation.

In the South, it is clear what Israel would hope to achieve by a ground offensive: putting a stop to the Kassam rocket attacks on Israeli civilians and smashing the radical Hamas' huge, ongoing military buildup in Gaza.

In the North, the reasons for the aerial operation remain a mystery. There are any number of theories.

Some Arab commentators suggest that Israel was testing an aerial route to Iran, whose nuclear aspirations are seen as a critical threat to Israel. Others suggest that it was testing new Syrian air defenses in a highly sensitive strategic area.

The air defense theory has some circumstantial support. According to the centrist Russian daily Nezavissimaya Gazeta, Syria started receiving sophisticated Russian-made Pantsir S-1E ground-to-air missiles a few weeks ago. The Russians agreed to sell Syria 50 Pantsir S-1E systems earlier in the year for an estimated $900 million.

The fact that Russia was quick to complain about the alleged Israeli incursion adds weight to the Pantsir theory. Russia expressed "extreme concern" at the Israeli violation of Syria's air space and called on Israel to respect international law.

According to this theory, the significance of the overflight -- if it took place -- is to show that even with the Pantsirs in place, sensitive Syrian strategic installations are vulnerable to Israeli airstrikes.

The Syrians say the Israeli warplanes came in from the Mediterranean over the port of Latakia, flying deep into northern Syria over Tel el-Abiad and Kamishli on the Syrian border with Turkey. This is the general area in which Syria has deliberately located chemical weapons' and Scud-D rocket factories ­ to keep them as far from Israel as possible and out of Israeli Air Force range. Syria's major oil fields at Deir e-Zour are nearby as well.

The Syrians have been trying to play down the significance of the Israeli achievement.

Mohammad Habash, a parliament member who often speaks for the regime, claimed that the Israeli planes had actually planned to attack Syrian targets, but had been beaten off by Syria's air defenses. He said the fact that Israel was not saying anything about the operation proved that it had failed.

"When Israel destroyed the Iraqi nuclear reactor in 1981, it was the first to say so," Habash declared.

Other Syrian spokesmen maintained that the incident showed nothing about Israel's long-range capabilities, arguing that the warplanes had taken off from nearby Turkish territory.

Israeli experts argue, however, that Turkey never would have sanctioned an Israeli violation of Syrian airspace from its territory.

"The new Islamist Turkish regime has very good relations with Syria," Israel's former foreign ministry director-general, Alon Liel, an expert on Turkey, told JTA. "If any military group in Turkey asked the political echelon for permission to do a thing like that, the answer would have been no. And if the Turkish air force had approved something like that without the political echelon's knowledge, the air force chief would have been fired within the hour."

Experts say that if fuel tanks from Israeli aircraft were dropped on Turkish territory, it probably occurred because the planes were operating near the Turkish border and not because they took off from bases in Turkey. The Israeli and Turkish air forces, which carry out periodic joint exercises, last did so two months ago in July.

Still, most Israeli military analysts do not think that Syrian President Bashar Assad will risk a retaliatory strike against Israel. They say if he doesn't attack, he might lose face, but if he does, he knows he could lose his hold on power. Given that stark choice, the analysts say, he will probably bite the bullet.

Nevertheless, the analysts warn, the possibility of a miscalculation or local incident triggering a wider conflagration cannot be excluded.

In the South, the probability of a military showdown is considered higher. There the initiative will likely be Israel's. Barak and most of the top army brass believe that sooner or later the Israel Defense Forces will have to go into Gaza to smash Hamas' growing military power. The longer they wait, they say, the more difficult it will be.

But some Cabinet ministers believe it might be possible to avoid a ground invasion if Israel finds a way to punish Gazans for Kassam attacks. Minister without Portfolio Haim Ramon, for example, proposes that every time a Kassam is fired, Israel should cut off electricity to Gaza. Gazans would thus be made to realize that rocketing Israeli civilians carries a price tag and might be deterred

The generals, however, are not enthusiastic about this approach. They say punishing civilians in this way would lead to an international outcry, and Israel would be forced to back down. Instead, they are proposing short, sharp pin-point attacks on Hamas militants and rocket-launching sites.

Already this approach has had some success: IDF forces captured 11 Kassam rocket launchers last week, and special forces kidnapped Mawash Abu Khader, a leading Hamas military operative, said to have been involved in the kidnap last year of Cpl. Gilad Shalit.

For now, the northern and southern fronts are both tense. But whereas Israeli analysts expect the confrontation with Syria to wind down, they predict Gaza will erupt some time after the planned regional peace summit in November.