Israeli Prime Minister Menahem Begin's proposals for autonomy on the West Bank "are unacceptable" to the Palestin Liberation Organization and should be even to "quislings" and "most Arab governments," PLO sources said today.

Commenting on Begin's news conference pronouncements in the United States, the sources also said "they should be unacceptable to (Egyptian President Anwar) Sadat unless he has decided to throw us to the dogs."

The sources noted only one half-encouraging sign - Begin's offer to let Palestinians settle inside Israel proper, Jonathan C. Randal of The Washington Post reported.

New services reported these developments:

Syrian President Hafez Assad met with PLO leaders last night in Damascus to review developments. In a Sunday Demonstration in the Syrian capital, more than 500,000 persons marched in protest against Sadat's moves, according to Damascus Radio.

In Riyadh, King Khalid of Saudi Arabia began talks with King Hussein of Jordan on ways to end divisions in the Arab world over the peace moves. Khalid also sent a message to the Arab League saying his country is mobilizing all its resources for Arab solidarity.

Arab League Secretary General Mahmoud Riad said Khalid was responding to a League message to all Arab leaders urging joint action to "face the dangers" of the Middle East situation.