Syrian missiles downed another Israeli reconnaissance plane today over Syrian territory just 25 miles west of here, military officials announced.

[The Israeli Army command said the plane was a pilotless drone and first maintained that it was hit as it flew over Lebanon's Bekaa Valley, just west of the Syrian border, but then said the craft, directed over the valley, may have directed over the valley, may have strayed into Syria. The Associated Press reported from Jerusalem.]

This is the third drone that Israel has acknowledged was shot down byh Syrian missiles and the sixth Israeli reconnaissance plane that Syria has claimed since the crisis over Syrian missiles in the Bekaa Valley began almost a month ago.

It is only the second time, however that Syria has claimed the plane it hit was flying over its own territory.The other claimed hits were reported to have taken place over Lebanon, where Syria has put 30,000 troops acting as an Arab Deterrent Force to prevent full-scale resumption of civil war.

Despite the bellicose words exchanged between Israel and Syria in recent weeks, the Jewish state has taken a low-key approach to the downing of its reconnaissance planes. Israel appears here to have gone out of its way not to increase tensions as would happen if it made a major issue out of the loss of the planes.

In all three cases that it has acknowledged its planes being hit, Israel has said they were downed by missiles fired from Syria -- not the ones Israel has demanded that Syria remove from the Bekaa Valley under threat of military attack.

Western diplomats here believe Syria purposely is using only the missiles stationed inside its own territory to shoot at the Israeli planes in effect sending a message to Israel that it does not really need the missile batteries inside Lebanon to protect itself.

Today's official Syrian announcement did not identify the Israeli plane as a drone. It said the craft was downed at 1:42 p.m. in the neighborhood of Zabadani, a village about five miles inside Syria's frontier with Lebanon.

Syrian officials, meanwhile, were awaiting the expected return here, possibly Tuesday, of special U.S. envoy Philip C. Habib, who has been reported to be waiting in Jerusalem for word from Saudi Arabia before deciding what to do next on his 18-day shuttle mission.

Washington Post correspondent William Claiborne reported from Jerusalem :

Habib did not meet with Israeli Prime Minister Menachem Begin, who said yesterday Habib is awaiting the replies from Saudi Arabia before continuing his diplomatic effort to avert another Middle East war.

Habib has visited Riyadh and reportedly obtained tentative Saudi approval of a compromise proposal that includes, among other elements, a Syrian commitment to withdraw its missiles from Lebanon and an Israeli undertaking to restrict its "operational" flights over eastern Lebanon. Begin said he will meet again with the U.S. envoy when the United States receives replies from Saudi Arabia.

Begin's allegation last night in a speech in Tel Aviv that Soviet military advisers are serving with Syrian troops in Lebanon, officially denied today by the Soviet Union, was immediately criticized by the opposition Labor Party as being an unnecessary public disclosure, if true.

Chaim Herzog, former chief of military intelligence and more recently Israel's ambassador to the United Nations, accused Begin of exacerbating the tension in Lebanon by making the statement. If Soviet advisers are there, Herzog said, disclosure by Israel will only make it more difficult to negotiate their withdrawal.

Begin said tonight that he is willing to go to Beirut "on 24 hours' notice," or to receive President Elias Sarkis of Lebanon in Jerusalem in an effort to resolve the crisis and sign an Israeli-Lebanese peace treaty.

In a reelection campaign appearance at the Migdal Haemek Kibbutz in northern Israel, Begin assured a cheering audience that the missile crisis will be resolved and that Israeli Air Force jets will be able to "fly freely over Lebanon" in the future.

Washington Post correspondent Jonathan C. Randal reported from Beirut :

In an apparently coordinated action early this morning, the American, Egyptian and Sudanese embassies in Beirut were attacked by rifle-launched grendades in what was presumed to be a gesture directed agains the Camp Davis peace treaty between Egypt and Israel.

The attack blew out windows on the second, third and fourth floors of the seaside American Embassy, but no U.S. diplomats were reported injured. One Egyptian Embassy employe received minor wounds, a spokesman said.