Prime Minister Menahem Begin held a special session of the Israeli Cabinet today to prepare for Wednesday's scheduled parliamentary debate on the peace proposals he has offered Egyptian President Anwar Sadat.

The failure of Foreign Minister Moshe Dayan to attend the meeting sparked speculation about a possible secret diplomatic initiative.

Another plausible reason for Dayan's absence however, was the possiblity he may have had a falling out with Begin following the Ismailia summit.

Israeli television said Dayan had "beyond all doubts" gone abroad and that the trip was planned before the weekend summit in Egypt. Speculation about such a journey focused on neighboring Jordan. Israeli leaders have secretly made such trips before to meet with King Hussein.

A Foreign Ministry spokesman said Dayan had been "busy," but said he did not know whether the foreign minister was in Israel.

Asked whether he knew why Dayan had not attended the Cabinet meeting. Begin said curtly, "Yes I know the reason," and walked away from reporters.

Officials did say that Dayan was at his home as of 7 p.m. this evening, Israel time.

Twenty-eight hours of Dayans' time was unaccounted for. He was last seen by journalists at about 3 p.m. yesterday, when he unceremonously walked out of a press conference being given by Begin upon their return from Egypt.

Dayan went on a secret mission in September. According to Israeli officials, Dayan met then in Paris with a representative of Morocco's King Hassan, a meeting that is credited with having set in motion the process that culminated in Sadat's breakthrough visit to Jerusalem Nov.19.

Dayan's press conference walkout yesterday followed an interview in which Dayan gave an extremely pessimistic account of the state of Israeli-Egyptian talks. That assessment contrasted sharply with a glowing account given by Begin at the press conference.

Those familiar with Dayan's thinking were today stressing how upset the foreign minister has been with the euphoria surrounding Israel's dealings with Egypt so far. They said he feels Israel has permitted Egypt to set the pace and to call most of the shots.

That there should be enough solid-seeming evidence to support several theories about what Dayan's absence meant is in itself a good measure of how much in the dark even the Israeli political elite has been kept about what is really transpiring.

It is stressed that Dayan's differences with Begin are serious but primarily practical - that the foreign minister feels that the prime minister has shown Sadat too many of the cards in Israel's hand and that this has allowed the Egyptian leader to control the negotiating game so far.

Earlier, however, there was a clash reported by the sources close to Dayan over Begin's failure to include a formal link to Jordan in the proposals for the future of the Israeli-occupied West Bank.

This difference seems to have been patched up, and informed sources say that soft-pedaling any mention of a role for Jordan has become more of a tactical device to try to draw Hussein's kingdom into the negotiating process rather than the difference in approach among the Israeli leaders that it was at first.

Dayan has stressed the need to bring Jordan into the picture as a way to keep the Palestine Liberation Organization out of it. Hussein and the PLO have been mortal enemies, and the Jordanian government could be counted on to make sure that the organization did not achieve any measure of control if the West Bank were no longer under Israeli military government.

High Israeli officials involved in the Israeli-Eygptian talks say that Israel favors an Israeli-Jordanian condominium over the West Bank similar to the old Anglo-Egyptian arrangement. When Britain and Egypt ruled the Sudan jointly, however, Egypt was virtually a British protectorate.

The conflicting signals about Dayan today could be part of a deliberate smoke screen. The French-language program of Israeli state radio said that Dayan stayed away from the Cabinet meeting because he had the grippe. English-language programs of the radio said it was because of "technical reasons."

The seemingly conflicting signals could be genuine. Relations between Begin and Dayan could indeed be as strained as all the surface indications suggest, but the foreign minister could nevertheless have carried out a special mission for the prime minister.

One close observer of the Israeli scene commented that there are so many tensions among the Israeli leaders that there is not enough natural, mutual trust to allow for an elaborate charade of disagreement.

Begin has yet to tell the Israeli public exactly what his proposals to Sadat involve. Before his trip to Egypt, Begin refused to give details on the ground that it was only polite to tell Sadat first. After the trip, he said that he was keeping the information back to tell the Parliament first, at the start of a debate on Wednesday.

There is now a line of speculation that Begin held back on releasing the proposals for an extra two days to allow Dayan to discuss them with Hussein first.

Sadat has said that he does not want to accept anything short of full statehood for the Palestinians of the West Bank. But, the speculation goes, Sadat may have told the Israelis privately that he could go along with their ideas for the West Bank if Hussein does.

Sadat has expressed great displeasure with the PLO, and it is unlikely that he is any more willing that Israel or Jordan to see the creation of a small, radical, territorially dissatisfied state between Tel Aviv and Amman.

Defense Minister Ezer Weizman, meeting with the parliamentary caucus of Likud, the conservative party that dominates the ruling coalition was reported to have said that the Israeli proposal for the West Bank and Gaza are both complete and final. He also reportedly said that Sadat really wants peace and that Israel must take risks to achieve it.

Apart from leaks of Weizman's report to the Likud caucus, practically no information was made available about this morning's cabinet session of more than four hours. Deputy Prime Minister Yigael Yadin did say, however, that the meeting was devoted primarily to a full report of the Ismailia conference without any debate.

Yadin told the 15 deputies of his Democratic Movement for Change that they may abstain in the parliamentary vote on Begin's peace proposals Wednesday but that they may not vote against the government. Begin has given his followers in the Likud freedom to vote as their consciences dictate, and a handful have already said they would vote "no."

A number of deputies of the Labor Party, the main opposition group, are reportedly planning to abstain.