The Israeli Cabinet unanimously approved Prime Minister Menahem Begin's Middle East peace plan today after incorporating several amendments apparently focusing on the crucial West Bank issue.

Emerging after the marathon Cabinet session, Begin refused to specify the modifications that were adopted. He asserted that his plan "in the main is the same" as the one he discussed with President Carter last week.

The approved version of Begin's plan, which he will present to Egyptian President Anwar Sadat on Sunday, is believed to have taken into account two points known to have caused concern to Israeli Foreign Minister Moshe Dayan.

Today's session lasted 7 1/2 hours - the longest meeting of the Begin cabinet - testifying to an extensive debate at the highest government level.

Begin was belived to have been persuaded to give ground on two points that concerned his foreign minister:

The pace of the negotiations, which Dayan is known to feel has so far been too fast for careful reflection to take place.

The need to create a tie between Jordan and the occupied West Bank. Dayan has maintained that unless the area is linked to Jordan, there is a grave risk that it will come under the control of the Palestine Liberation Organization.

Begin has been suggesting that the West Bank could be an autonomous entity without becoming an indepedent state or being placed under the sovereignty of Jordan or Israel.

The official Cabinet communique said explicitly that the government had approved the Begin plan of "administrative autonomy" for the West Bank. In news conference statements in Hebrew and English, Begin stressed the unanimous approval he received from his 16-member Cabinet.

Contrary to the usual practice, however, this was not explicitly stated in the Cabinet communique.

The communique said that Begin will be accompanied to Egypt by the Cabinet's two strongmen - Foreign Minister Dayan and Defense Minister Ezer Weizman. No other ministers were listed as part of the Israeli delegation, although the Egyptians earlier today issued a long list of participants from their side.

It had been widely expected that Deputy Prime Minister Yigael Yadin, head of the ruling coalition's left wing, the Democratic Movement for Change, would be included. Also tipped to go was Agriculture Minister Ariel Sharon, the commander of the tank units that crossed the Suez Canal in the 1973 war, turning the tide of battle in Israel's favor.

There has been speculation that Begin would try to enlist Labor Party opposition leader Shimon Peres into the delegation as well. This possibility is still open and awaits the outcome of the prime minister's meeting Friday with the foreign affairs and defense committees of Parliament.

Members of Parliament have been openly expressing their dismay at being kept in the dark by Begin - dismay that was also being expressed in private by Cabinet ministers.

Asked whether the fears of some ministers about his peace plan had been dispelled, Begin replied, "Ask those ministers that you say had suspicions and fears."

Begin said that the changes to his plan did not alter its mainlines, which generally follow ideas that Dayan has been advocating for years.

"Of course," Begin said, "when there is a discussion, there are proposals, there are opinions expressed. The discussion as far as I am concerned, with my long experience - I am an old Jew now of 64 - was one of the best, on the highest level, I have ever participated in, and, ultimately, we took a unanimous decision."

"Some amendments were adopted," he said, "but in the main this is the same peace plan that brought to the knowledge of the President of the United States, and will bring it to the knowledge of the president of Egypt on Sunday at Ismailia."

The only question that Begin sidestepped in both his press conferences was whether Jordan would have a link with the West Bank. His refusal to discuss the subject in any form immediately aroused speculation that it was one of the sensitive points of debate in the Cabinet and that the prime minister had been forced to shift his ground to give Jordan a role.

One reason he has resisted this is because of his own Likud group's ideological commitment to bringing the West Bank under Israeli sovereignty. By suggesting that it should be under no sovereignty at all, let alone Jordanian sovereignty, Begin is talking a big gamble on the loyalty of his closest supporters.

During the Cabinet session, a small [WORD ILLEGIBLE] of followers of Gush Emunim (literally faith bloc), the most militantly annexationist part of Begin's political constituency, demonstrated outside in the driving rain.

"I love the members of the Gush Emunim," said Begin. "But their demonstration is pointless. They have no justification."

Representatives of Israeli settlers on the West Bank requested an urgent meeting with Begin to get assurances that they will remain under Israeli rule.

While Begin defended the pace of the negotiations in Hebrew, saying, "we want to keep a fast pace," to a more indirect question about it in English, he changed his emphasis considerably.

"A peacemaking process is not a matter of a day," he said. "I heard that a member of the Egyptian government expressed his opinion that this negotiation may last a few months. I agree with him."

Begin also volunteered information on what seemed to be a new procedural wrinkle more in line with Dayans lets-take-it-easy approach. The prime minister said he planned to propose to Sadat the formation of "working committees on various subjects."

"I hope this logical proposal will be accepted," Begin said. This seemed to suggest that it is a new idea that could be unfamiliar to Sadat.

The essential outlines of the Begin proposals are probably already known to Sadat from the Carter administration's account of what Begin has told them or, even more recently, from the talks Weizman held Tuesday and Wednesday with Sadat and Egyptian War Minister Mohammed Gamassi.

Begin has said that he plans to submit "a detailed plan" on Christmas Day. He said it would include maps, presumably of the special security zones Israel reportedly seeks in the Sinai Peninsula.

Begin said today he had not heard Sadat's statement against accepting continued Israeli military presence in Sinai and the West Bank. The Israeli press and the Israeli state radio have been discounting those statements, suggesting that Egypt would be willing to allow long timetable during which the Israelis could continue a "temporary" occupation of strategic points.

Begin repeatedly stressed that Israel is prepared to discuss Egyptian counter-proposals. "Our peace plan is not a blueprint," he said.

In another development, Foreign Ministry officials said that Dayan plans to visit Italy in January and that he would have an audience with the Pope. The sources said they assumed that there would be a discussion with the pontiff about the status of the Christian holy places in Jerusalem in any final peace settlement.