Amid the deadlocked negotiations over the withdrawal of Palestinian guerrillas from West Beirut, Syria has dramatically signaled Israel that it is still a political and military power to be reckoned with in Lebanon.

The appearance of highly sophisticated Soviet SA8 ground-to-air missiles in Syrian-controlled areas of Lebanon's eastern Bekaa Valley and Syria's threat to use "all types of weapons" to make the Israelis suffer "in human lives and equipment in a way they never expected" are not being taken lightly here.

Israeli warplanes yesterday destroyed three batteries of the highly mobile SA8s north of the Beirut-to-Damascus highway, and the government today again stressed its determination to prevent Syria from introducing any missiles into Lebanon.

After today's Israeli Cabinet meeting, Cabinet Secretary Dan Meridor told reporters that "very grievous consequences" would result if Syria attempted to retaliate against Israel for yesterday's air raids.

Israeli radio said the Cabinet heard intelligence reports on the situation in the Bekaa and an assessment of Syrian intentions that reportedly concluded that Syria was acting primarily to stake its claim to the Bekaa and to defend itself from a possible Israeli strike against its own territory. The consensus was, it said, that Syria was not planning an offensive campaign and that an all-out war could be averted.

Earlier, an Israeli official said that Israel had no intention of or interest in fighting Syria and that it expected Damascus to keep the cease-fire and help halt Palestinian guerrilla infiltrations from Syrian-controlled areas of the Bekaa.

"If they keep the cease-fire, obviously we will too," he said.

Israeli analysts believe Syrian President Hafez Assad has seized upon the issue of a new haven for the Palestinian guerrillas and their leaders to inject himself into the Beirut negotiations as a prelude to forcing his way back into any forthcoming U.S.-sponsored Middle East peace talks.

"Damascus has grasped the opportunity to put itself back on the map and influence developments," said one analyst. Thursday's renewed fighting in the Bekaa was just "a stage in the Israeli-Syrian confrontation over Lebanon," he added.

"The main message was, 'You won't find any solution to Beirut without our approval and taking into account our interest,' " he said. "They are waging a campaign to put themselves on the map for the future settlement of the Middle East."

The fact that Damascus moved the missiles in is being interpreted here as an unexpected hardening in Syrian policy that could not have been undertaken without explicit Soviet approval and support.

In Beirut, the Christian radio station reported yesterday that Syria was bringing reinforcements into the Bekaa accompanied by East Bloc personnel. But an Israeli military spokesman today would not confirm this report.

The new intensification in tension between Syria and Israel and the threat of another round of fighting come against a backdrop of mounting Israeli concern about the infiltration of Palestinian guerrillas from Syrian-controlled areas behind Israeli lines.

Even before the latest "missile crisis," this development had raised in stark terms the question of whether there could ever be an enduring settlement of the guerrilla presence in Lebanon without a prior Syrian-Israeli agreement about their respective future roles in that war-fragmented nation.

In the past three weeks, Syria has been signaling Tel Aviv that it is well within its capabilities and political will to unleash a "war of attrition" by proxy against the Israeli Army in southern Lebanon, making use of the Palestinian guerrillas.

Israeli military sources say there are "thousands" of guerrillas behind Syrian lines. Some were already there before the invasion began and others fled there to escape the initial Israeli blitz through southern Lebanon.

In justifying its Thursday raid, the Israeli Army said that 10 of its soldiers already had been killed on the Bekaa Valley front and 13 others wounded, while 29 guerrillas had died in 75 incidents since the first cease-fire began June 11.

To all appearances, Syria, just as it did long before the invasion, has every intention of using the Palestinian guerrilla presence in Lebanon as one of its major trump cards in forcing Israel and the United States to deal with it as a regional power.

But there is more at stake for Syria than just the game of Middle East peace politics. The Bekaa Valley, once part of "greater Syria" as was most of Lebanon, is strategically Syria's "soft underbelly," the corridor leading not only to Damascus but to the rich agricultural and industrial areas around Homs at the northern end of the valley.

Israeli analysts say Assad has committed about one-half of his 225,000-man Army to holding the Bekaa, with the bulk of its forces located to the north of the vital Beirut-to-Damascus highway. In the valley, this road is still under Syrian control.

According to an Israeli Army communique Thursday, the Syrians are building fortifications in the Bekaa "at a feverish pitch." Included are antitank trenches, ramps for tank fire, earthen walls to protect its armor, minefields and artillery and antitank positions.

Israeli military spokesmen say the main infiltration route for the Palestinian guerrillas is in the southern Bekaa, where Syrian and Israeli forces are up against each other roughly eight miles northeast of Lake Qirawn along the two parallel roads leading through the valley.

The Israelis broke through the mountainous Chouf region southeast of Beirut to seize a long strip of the Damascus highway from the Lebanese capital to the outskirts of Sofar, more than halfway to the Bekaa.

But they never succeeded in pushing their easternmost column of armor and troops through Syrian defenses to take control of this vital east-west road link across the valley.

Thus, the Syrians are still holding a jagged line all across the Bekaa eight to ten miles south of the road.

Assad's commitment of so large a part of his Army to the Bekaa is all the more striking since it has no effective air or missile coverage. It is a sitting duck for Israeli warplanes.

But it illustrates the Syrian leader's grim determination to hold on militarily to at least part of the Bekaa and politically to Syria's much reduced presence in Lebanon.

Together with the talk of a possible U.S.-PLO dialogue, Syria's new assertiveness has made the Israelis increasingly nervous as the trend of events moves away from the seemingly simple questions of when the Palestinian guerrillas will leave Lebanon and where they will go toward larger political issues of an overall settlement.

This is partly because the more the bigger questions are discussed--and the United States, Syria, Saudi Arabia and possibly even the Palestine Liberation Organization become involved--the less control the Israelis have over the outcome.

But it is also because they fear these questions may in the end be resolved in ways deemed by the Israeli government to be compromising. This anxiety is reflected in the Israeli media, where commentators viewed uncomfortably last Tuesday's visit of Syrian Foreign Minister Abdul Halim Khaddam as a sign of change in previously hostile U.S.-Syrian relations.

Zeev Schiff, the respected military correspondent of the newspaper Ha'aretz, suggested that Damascus, like the PLO, was seeking its political recompense from the United States for its military defeat at Israeli hands in Lebanon.

"The reward from Syria's viewpoint is not only what the Palestinians will get should they move their headquarters from Beirut, but the role Damascus will play in any settlement in Lebanon," Schiff wrote.

Israel's military leaders, acutely aware that they are facing a potential political disaster, are now weighing whether to act militarily to short-circuit this trend of events.

What is happening in the Bekaa Valley, as Schiff noted, could be a good pretext for launching an assault on the guerrillas trapped in West Beirut and on the Syrian forces in eastern Lebanon. Israel has put Syria and the PLO on notice that it is seriously considering this option.

Whatever the government of Prime Minister Menachem Begin decides, Israel and Syria are going to have to deal with each other, presumably once again through U.S. mediators. There is already a school of thought here that the two will agree to a trade-off in which Israel will recognize Syria's vital security interests in the Bekaa and Syria will agree to recognize Israel's in southern Lebanon.

This trade-off, suggested one Israeli analyst, might even involve Syria's concession of the strategic Golan Heights to Israel, which has already annexed the area anyway, while Israel acquiesces in Syria's de facto annexation of the northern Bekaa.

Whether this is a pipe dream or Middle East realpolitik it is perhaps too soon to judge. But it is certain that some Israeli policy makers do not rule it out as the basis for an agreement with this longtime enemy.