Israel today broadened its warning to Syria not to move into areas of Lebanon evacuated by the Israeli Army to include the Syrian-backed Druze militias in the Chouf mountains.

An Israeli official, at a briefing for foreign correspondents, said that there was in effect a "red line" in Lebanon over which the Syrians and their Druze allies should not attempt to pass.

He was not specific, but, in response to questions, mentioned the Chouf mountain Christian village of Bhamdun and the Beirut-to-Damascus highway nearby.

The official also did not specify what action Israel would take in the case of a Syrian or Druze advance into the evacuated areas, but he did not rule out a military response such as yesterday's strafing runs by Israeli jets against Syrian-supplied tanks that were apparently manned by Druze militiamen.

"Internal things are one thing, but extension of Syrian territory is another," he said. "Any act which will be seen as an extension of Syrian territory will be considered in the context of the moment. The Syrians have been warned."

After two U.S. marines were killed in Lebanon last week, a senior White House official told reporters that the Syrians' refusal to withdraw from eastern Lebanon was a "complicating factor" in the violence there.

Reuter news service reported from Damascus that Syria called on the Arab League to sever all diplomatic, economic, cultural and political ties with Lebanon because it had signed a withdrawal agreement with Israel May 17, "making Lebanon an Israeli protectorate."

Speaking of the Druze in the Chouf mountains, the Israeli official said, "They are supported by Syrian weapons and training. Syria should be cautious. Israel has given its warning."

The official said the fighting raging in the Chouf mountains is seen by Israel "all as a Syrian attempt to expand its power . . . . It's not the Druze, it's the Syrians."

The official added that the fall of Bhamdun to Druze forces would be seen by Israel as "a change in the status quo, extending Syrian territory."

The warning regarding the Druze militias appeared to put them in the same category the Israelis have always applied to the Palestinian guerrillas that operate behind Syrian lines in eastern Lebanon--as puppets of the Syrians for whom Syria should be held responsible.

The official's statement was an elaboration on the warning voiced yesterday by Defense Minister Moshe Arens after the Israeli jets attacked the Druze-manned tanks in the first hours after the Israeli withdrawal from the Chouf mountains.

Arens said at a news conference last night that "since these tanks came from across the dividing line between us and the Syrian forces, the Israeli Air Force was called into action to fire some warning shots." He said Israel has "made it clear that we do not want hostile forces entering the areas we leave" and added that "it should be clear to the Syrians that that includes them."

Both Arens and Army Chief of Staff Lt. Gen. Moshe Levy said yesterday there was no evidence of direct Syrian involvement in the renewed Chouf mountains fighting. But the Israelis clearly believe that the Syrians hope to use the Druze as their proxies in the area, and this belief led the Israelis to extend their warning about "hostile forces" to include the Druze militias.

"To the best of my knowledge, even though there was shooting from the area under Syrian control, there has been no active Syrian participation" in the fighting, Levy said. "But it's clear that shooting from their territory is significant in terms of the permission to engage in this shooting."

Except for a brief period of tension last spring, the Syrians have been for months extremely cautious in Lebanon and have appeared determined not to heat up the situation while Israel's patience with its policeman's role amid the bitter sectarian rivalries of the Chouf grew thin, finally leading to yesterday's partial withdrawal to new positions farther south.

But now, with the Israelis gone and the Chouf engulfed in renewed fighting between Lebanese Christians and Druze, the Israelis clearly believe the Syrians hope to use the Druze to extend their influence in Lebanon and eventually topple the government of President Amin Gemayel.

In withdrawing from its previous line in central Lebanon, Israel limited the military role it can play in the current fighting. It could not return its ground forces to the Chouf without risking casualties and a domestic uproar.

But as yesterday's brief strafing run by the Israeli jets was apparently meant to demonstrate, Israel maintains virtually complete air supremacy in the skies over Lebanon and in the past has never been reluctant to use its Air Force against targets there.

At the same time, Israeli air strikes against Syrian targets because of advances by Druze forces would risk turning the century-old Christian-Druze feud in the Chouf mountains into another direct Israeli-Syrian conflict.