The Palestine Liberation Organization leadership is more open-minded about Israeli Prime Minister Menahem Begin's plans for the West Bank and the Gaza Strip than its formal condemnations of his statements indicate, guerrilla sources said today.

The nuances in PLO thinking do not reflect any visible degree of satisfaction with any particular aspect of Begin's explanations on American television yesterday.

Rather, they are based on the feeling that Begin will have to give much more to prevent the Cairo talks from failing.

Public statements reflected a position of hard-line rejection.

Majed Abu Sharar, a PLO official spokesman, said Begin's plan was "null and void because it is based on the thesis of continued occupation and expansion" and it rules out an independent Palestinian ministate on the West Bank and in Gaza.

The PLO news agency, WAFA, wrote the Begin proposals off as "ridiculous and insulting."

More symptomatic of the PLO mood, however, is continued secret communication with Egyptian President Anwar Sadat, despite public charges he is a traitor.

PLO sources realize that for Israeli domestic political consumption, Begin cannot be seen to be offering basic concessions without being forced to do so either by a tough Egyptian stand or American pressure or both.

Whatever its doubts, the PLO knows it is so weak that it has little choice but to hedge its bets and hope.

The PLO position is complicated by its own recent formal alignment with the hard-line theses of the "rejection front" that opposed any dealings with Israel. Nor does the rigid intransigence of its Syrian ally and protector make matters easier for PLO maneuvering.

Still, PLO moderates make no secret of Yasser Arafat's willingness to participate in peace negotiations despite the hard-line pact - if Begin makes the necessary concessions.

Implicit in such a strategy would be the end of the hard-line pact signed earlier this month in Tripoli and a likely split within the PLO itself.

The PLO is worried that its hard-line stance will somehow prove to be the pretext for depriving it of its position as the recognized representative of the Palestinian people.

The sources said Sadat and Israel could cite formal PLO instransigence to hand over the West Bank either to King Hussein of Jordan or to West Bank residents loyal to him.

Thus, the timing of any PLO change of policy may end up being as important as the move itself, the sources suggested.

In other developments, news services reported:

The official radio of Saudi Arabia, an important financial backer of Egypt, said in a commentary on Begin's proposals that there is no justification for optimism "as long as Israeli occupation of Arab territory and Jerusalem continues . . . This occupation is a dagger stuck in the heart of the Arab nation . . . the dagger must be removed through Arab unity and cooperation"

Syria's official radio, saying the Begin plan "actually is designed to retain Israeli occupation of the West Bank and the Gaza Strip," also denounced the proposals for not allowing for creation of a Palestinian state.

West Bank Arab leaders reacted with hositility to the Begin plan. "It's not giving us anything," said a key official in Tulkarem, a town that used to be just inside Jordan before the 1967 war. "The Israeli army and Israeli settlements will remain in the area. This we cannot accept," the official said.

Mayor Karim Khalaf of Ramallah said, "We don't want federation with Jordan. If Israeli settlements are allowed there will be thousands of Israelis on our land within 20 years."

Elias Freij, mayor of Bethlehem, said he thought there must be more to the plan. "If that's all there is, we reject it entirely," he said.

At the United Nations, PLO observer Zehdi Labib Terzibib, attacked President Carter as well as Begin. "President Carter seems to have forgotten about the human problem" of Palestinian refugees, he said. "It is the neutron bomb mentality; kill the people but keep the buildings."

Lebanese authorities dismantled a powerful time bomb shortly before it was set to explode at the Egyptian embassy in Beirut. Sunday night, a bomb shattered glass at the downtown Bank of Egypt and Lebanon.

King Hussein of Jordan arrived in Bahrain on a Persian Gulf tour that already has taken him to Saudi Arabia and Kuwait. He reportedly is seeking further Arab support for Egyptian President Anwar Sadat's peace initiatives.