Syrian Information Minister Ahmed Iskandar Ahmed said today Syrian troops would not withdraw from Lebanon "under the guns of Israeli tanks," but would consider a withdrawal request by Lebanese authorities if they were able to make it of their "free will."

Ahmed said at a news conference that the Lebanese request for a Syrian withdrawal was rejected on the ground that it had been "dictated" to Lebanese President Elias Sarkis by Israeli forces surrounding his presidential palace in the hills southeast of Beirut. Ahmed said a similar demand, relayed by the Israelis through Lebanese Gen. Samir Khatib, had been rejected less than two days before.

Syrian troops invaded Lebanon in 1976 to stop a civil war, and the Arab League later created an Arab Deterrent Force, made up mostly of Syrian units, to keep the peace.

The essentially Syrian force is nominally commanded by Khatid and answerable to Sarkis, and Syrian authorities always have said that it would be withdrawn if the Lebanese government so requested. However, Ahmed's statement today made clear that Syria is committed to keeping troops in Lebanon regardless of the Lebanese government's position.

Ahmed also said that Syrian troops still in Beirut would resist any Israeli attempts to attack Palestinian strongholds in the city's predominantly Moslem western section.

However, diplomatic sources here believe the Syrians are not in a position to defend Beirut and probably would not risk a major break in the cease-fire to try to do so. The Syrians are more likely to fight to defend Lebanon's Bekaa Valley, which runs along Syria's western border, if the Israelis try to make good their demand that all Syrian forces leave Lebanon, the diplomat said.

In his news conference, Ahmed declined to say whether the Syrians would resume fighting in Lebanon as a whole if the Israelis did not withdraw as stipulated by Damascus as the "basis" for accepting the June 11 cease-fire.