Cloaked in extraordinary secrecy, the Israeli navy attack Thursday night on West Beirut was still being officially explained last night as a pre-emptive strike against Palestinian terrorists, but government sources freely admitted in private that the purpose was to warn Syria against further bombardment of Christian strongholds in the Lebanese capital.

As they held intensive discussions on the worsening situation in Beirut, Israeli defense officials said the next 24 to 48 hours will be crucial in determining whether Syria will heed the warning and ease the pressure on the Israeli-supported Christian militias.

"Of course it's a warning action. The first time you act in a territory or place where the Syrian army is, it is a warning out front," a Defense Ministry official said.

While the attack appeared to reflect a shift in Israeli foreign policy toward Syria - moving from veiled threats and harmless overflights by Israeli warplanes to direct military intervention - government sources maintained that was not the case.

They emphasized that Thursday night's strike could be construed as an indirect intervention, aimed at familiar Palestinian adversaries and representing little more than escalation of the common Israeli technique of sending jet fighters screaming at supersonic speeds and at rooftop level over downtown Beirut to convey a message of warning to the Syrians.

Also, it was noted, the attack would serve to signal to Western powers, particularly the United States and France, Israel's sense of urgency in the need to apply more diplomatic pressure on Syria.

At the same time, it served notice to the Syrians that Israel's military might can be applied, if necessary, from a number of different directions, thereby putting the already overextended Syrian army off balance in its deployment.#TAlthough the official posture of the government yesterday held to the line that the target of the 90-minute attack from the three missile vessels was strategic Palestine Liberation Organization strongholds, government sources said Syrian positions undoubtedly fell under fire. But the government refused to release details of post-strike analysis.

"If you bomb with the cannon from a ship, who knows if you miss the PLO and hit something else," said a defense official.

The government would not confirm the numbers of ships involved, the duration of the attack and the areas pinpointed in advance as targets.

However, state-owned Israel Radio, quoting information it said it had received from Beirut, said the targets included Syrian positions between the Christian port of Junia and Beirut, as well as other syrian ground forces. Israel Radio, like all other media in Israel is ubject to military censorship.

Military sources said that about 100 rounds were fired during the operation and that the navy scored "good hits." Israel, according to Jane's Registry of Ships, has 12 missile vessels equipped with 40MM and 75MM radar-controlled rockets.

Military officials also refused to discuss foreign reports that the missile ships may have used the barrage as a cover to unload supplies - and even Christian reinforcements from southern Lebanon.One government spokesman denied emphatically a report that Israeli troops had been landed.

Israel has long supplied arms to the beseiged Christians, and has helped keep supply lines open at the port of Junia.

Officially, the government was not going beyond its terse communique issued shortly before midnight last night, declaring that navy vessels had "shelled a Fatah costal base in the southwestern sector of Beirut." Fatah is the largest group within the PLO.

There was nothing in the statement to connect the action to the Syrian army, and government officials yesterday sought to convey the impression that the Fatah base was somehow linked to the PLO attempt on Saturday to sneak a freighter loaded with explosives and rocket launchers into the Gulf of Acqaba for an attack on the Sinai coastal town of Eilat.

Israeli navy vessels sank the freighter, which military officials said had been outfitted in the Syrian port of Ladakiya.

A Defense Ministry spokesman last night said Thursday night's Beirut attack had hit a hotel used by Palestinian terrorist groups.

During the operation, it was learned, Defense Minister Ezer Weizman, Chief of Staff Rafael Eitan and intelligence chief Shlomo Gazit followed reports at the Defense Ministry, and Weizman radioed his congratulations to the vessels.

Yesterday, the three top defense officials briefed the foreign affairs and defense committee of the Knesset, Israel's parliament. Although the meeting was closed, it was understood that the three officials made it clear to the committee that Israel will not be able to exercise restraint indefinitely if the Syrian attacks continue.

Deputy Prime Minister Yigael Yadin, in an interview in Radio Israel, said that despite the political restraints stemming from the Camp David summit conference, Israel is obligated not to let the Christians be bombarded indefinitely.

Asked if Syria's pupose is to scuttle the Camp David agreements, Yadin cited a "coincidence" of timing, and added, 'There exists Israel's publicly-made obligation not to let the Christian community be annihilated."