Syria today announced a noon cease-fire with Israeli forces in Lebanon with the demand that it be accompanied by "complete Israeli withdrawal" from the war-ravaged neighboring state.

In making its announcement, the Syrian government did not explicitly draw a link to an Israeli withdrawal but instead referred to a meeting last night between President Hafez Assad and U.S. special Middle East envoy Philip Habib in which Syria said it had stipulated a complete Israeli withdrawal from Lebanon as the basis for a cease-fire.

A government spokesman here said today that Habib had flown to Israel this morning with Syria's "conditions" for an agreement ending the six days of heavy fighting in Lebanon since Israel's invasion. The spokesman declined to elaborate on the "conditions," and the time frame for the withdrawal demanded by Syria remained unclear. Israel has set no time limit for its forces to remain in Lebanon.

The comments appeared to indicate that Habib's shuttle diplomacy was continuing.

The cease-fire apparently was being observed by both sides this afternoon in Lebanon's Bekaa Valley, the scene of heavy fighting this morning as Israeli warplanes struck targets defending a vital highway from Damascus to Beirut.

Battle claims by the two sides about this morning's fighting remained widely at variance. Syria's state-run television tonight said its forces had shot down two French-built Israeli Mirage fighter bombers this morning near the Syrian-Lebanese border and a reconnaissance drone over Damascus. It also said Syrian troops had knocked out 40 Israeli tanks, but did not specify when. The report did not mention Syrian losses. Israel said it had shot down 18 Syrian aircraft today, losing none of its own.

In a separate announcement, a military spokesman yesterday said Syrian forces had inflicted heavy casualties and materiel losses on the Israelis in artillery, tank and air battles. He said the Israeli advance up the Bekaa Valley had been halted by helicopter-borne Syrian troops. The spokesman said Syria's helicopter gunships had destroyed 55 Israeli tanks and an assortment of other equipment. In all, he said, Israeli losses yesterday included six warplanes and 164 tanks and armored vehicles.

As if to lend credence to the claims, the military spokesman also listed surprisingly heavy losses by Syria's own forces, including six helicopters, seven Mig fighter planes, 83 tanks and two missile batteries.

Israel said it shot down more than 20 Syrian planes yesterday and has knocked out all 19 of Syria's surface-to-air missile batteries in the Bekaa Valley.

The Syrian television broadcast tonight repeatedly praised its forces' battle against "U.S. imperialism" in defense of Lebanon, the Palestinians and the Arab cause. According to a Western diplomat here, however, there has been no sign of any serious anti-American feeling among the public because of the fighting in Lebanon.

In fact, Damascus appeared decidedly normal and relaxed on this calm, Moslem sabbath. While there has been "a certain amount of tension" in the capital this week, one diplomat said, there has been no sign here of any Syrian "war fever." Traffic has been normal, shops have stayed open with no sign of hoarding, the city has remained lit up at night and there has been no evidence of any civil defense measures.

The Syrian acceptance of the cease-fire appeared to put Damascus at odds with the Palestine Liberation Organization, which has said that resistance to the Israeli invasion will continue.

Apparently caught up in the divergence late this morning were a half dozen busloads of Palestinians from Jordan waiting to cross into Syria at the Dera border point.

The Palestinians, mostly youths, appeared eager to head north to Damascus and then cross into Lebanon to join PLO fighters. But their buses, plastered with posters of PLO leader Yasser Arafat and flying Palestinian flags, remained parked at the border crossing point for more than two hours, and it was not known whether they ever were allowed through.

Syrian soldiers interviewed at the border crossing point of Jdeideh late this afternoon said the Bekaa Valley had been quiet since the cease-fire took effect and that the road to Beirut was still open.

Some Arab troops seemed to treat the cease-fire as a sort of victory following the swift Israeli sweep through southern Lebanon to within striking distance of the Beirut-Damascus highway, the main lifeline of the Syrian forces stationed in Lebanon.

Palestinian guerrillas seen riding back from the Bekaa Valley toward Damascus atop a Syrian armored personnel carrier and a truck waved Palestinian flags and flashed victory signs as they fired their Soviet Kalashnikov assault rifles in the air in triumph.

Syrian armored vehicles and truckloads of troops moved on the road in both directions in no apparent pattern of withdrawal or reinforcement of the forces in the Bekaa Valley.

Today's cease-fire announcement came in marked contrast to a presidential message to the Syrian armed forces published this morning in which Gen. Assad called on his troops to fight on to "victory or death."