Israeli Air Force jets attacked Syrian SA9 missile batteries guarding the Bekaa Valley again today in a new warning against the continued Syrian and Palestine Liberation Organization presence in northeastern Lebanon.

Israeli military spokesmen said their planes knocked out four mobile antiaircraft missile batteries at Dahr al Baydar, six miles east of Bhamdun, a mountain town that is Israel's forwardmost position along the Beirut-Damascus Highway leading to the Syrian-occupied Bekaa Valley.

It was the second consecutive day of Israeli air strikes against the missile emplacements defending Syrian positions across from Bhamdun, near where PLO units last weekend captured eight Israeli soldiers. Wednesday, Israel reported knocking out one SA9 battery in the same vicinity.

The Israeli air strikes underline the escalating tension along the Syrian-Israeli cease-fire lines east of Beirut in the wake of the capture of the Israeli soldiers. The PLO has announced it is holding the Israelis as prisoners of war to be exchanged for some of the thousands of PLO prisoners captured by Israel after its June 6 invasion of Lebanon.

Since the PLO completed its evacuation from West Beirut last week in compliance with an agreement negotiated by U.S. special envoy Philip C. Habib, the Bekaa Valley has become the new confrontation line between Israel and the PLO.

Israel, which has said it will not withdraw its Army from Lebanon until Syria and the PLO do likewise, has repeatedly warned Syria in recent days about breaking the shaky cease-fire it agreed to June 11. The Israelis had neutralized the Syrian Air Force as their troops advanced for the siege of West Beirut.

Small PLO units, operating from behind the Syrian lines in the Bekaa, have made a series of attacks in recent weeks on isolated Israeli positions, ambushed patrols on back country roads, and planted mines that have wounded Israeli soldiers.

Israeli Defense Minister Ariel Sharon warned Syria earlier this week that Israel held Damascus responsible for the PLO actions and the capture of its soldiers. The air raids over the past two days are believed to have been ordered to underline Israel's impatience with the situation in the Bekaa.

Syria is entrenched in the valley with a force of 25,000 men, and an estimated 9,000 to 10,000 PLO irregulars behind their lines, many of them recent evacuees from Beirut who have drifted back into Lebanon from Syria.

PLO leaders evacuated from Beirut earlier this month have made recent, well-publicized visits to PLO units in the Bekaa and the Syrian-dominated northern Lebanese port of Tripoli.

PLO Chairman Yasser Arafat's deputy, Salah Khalaf, the last senior PLO leader to leave Beirut last week, appeared in Tripoli early this week to declare that the PLO's departure from Lebanon had only been to save it from further Israeli bombings. He declared that "Beirut is still our capital."

Other visitors include George Habash, leader of the Popular Front for the Liberation of Palestine, and the Marxist Nayef Hawatmeh, who tonight delivered a heated speech in a Palestinian refugee camp north of Tripoli after visiting the Bekaa to inspect PLO units there.

U.S. officials have privately been urging both Syria and Israel to preserve their cease-fire and avoid any open hostilities pending a resumption of the American mission, now to be headed by Deputy Assistant Secretary of State Morris Draper. The United States hopes to be able to work out an agreement for the withdrawal of Syrian, PLO and Israeli troops from Lebanon in the same way it negotiated the PLO evacuation from Beirut this summer.

Habib has expressed the hope that the total withdrawal of all foreign troops from Lebanon might be accomplished by the end of the year. U.S. officials, however, privately say that negotiating such a withdrawal will be much more complex than the PLO evacuation from West Beirut.

Meanwhile, the normalization of Moslem West Beirut continued, with the Lebanese Army taking up positions around, and then in, the bombed-out Palestinian refugee camp of Burj al Barajinah on the southern outskirts of Beirut, just east of the Israeli-occupied international airport. The camp had been a major bastion of the PLO during Israel's siege of West Beirut.

The takeover was marred by a shooting incident. Some Palestinians, of an unknown group, in the camp refused to give up their sidearms, which they said they needed for self-defense. The Palestinians exchanged shots with an Army partrol, then fled, leaving one wounded man.

President-elect Bashir Gemayel, the Christian Maronite militia leader who is to be inaugurated as president Sept. 23, warned neighboring countries with subsidized newspapers in Beirut -- to proselytize their views -- that they will not be allowed to have them after he takes power.

"If those states want newspapers," Gemayel said, "they should found them on their own territory. Those who want to spread their ideas here of politics of refusal, or steadfast, or whatnot, should do so on their own territory, not here."