Israel is beginning to pull out all the stops to try to block what it fears will be the next big US concession to Saudi Arabia in the wake of the sale of sophisticated AWACS planes to that country.
That next concession, already shaping up in Israeli eyes, would be US support for Saudi Crown Prince Fahd's eight-point peace plan for the Middle East.
The urgency with which Israel feels it must move to prevent this is indicated by Israeli Prime Minister Menachem Begin's response, sent Oct. 30, to President Reagan's letter of assurance of continued US support of Israel in the wake of the Saudi AWACS deal.
Mr. Reagan had not mentioned the Saudi peace plan in his letter, but that is what Mr. Begin concentrated on in his reply. The plan, Mr. Begin said, was formulated in a sophisticated way but was aimed at Israel's gradual destruction in phases. He called on Mr. Reagan to remain faithful to Camp David as the only basis for peace in the Middle East.
Israel's Ambassador to the US, Ephraim Evron, has already made parallel representations to US Secretary of State Alexander M. Haig Jr. And Mr. Begin is scheduled to make an important speech in the Israeli Parliament Nov. 2, in which he is expected to bluntly state Israel's fears that the US will henceforward use Saudi Arabia as a main pivot of its Middle East policy -- at Israel's expense.
When Mr. Begin called on Mr. Reagan to stick to Camp David he was clearly aiming to head off a process that the latest issue of the Economist newspaper describes as ''cutting Camp David in half.'' Western and particularly US acceptance of parts of the Saudi plan would be the means for doing this.
French Foreign Minister Claude Cheysson, using a different phraseology, has raised the same possibility. He has spoken of the need for ''a bridge'' once the ''useful'' part of Camp David is completed to what thereafter needs to be done.
According to this line of thinking, the ''useful'' part of Camp David, due to be completed April 26, is the securing of the final Israeli withdrawal from Sinai. When the French and other Europeans talk about what needs to be done thereafter, they mean securing Israeli withdrawal from the West Bank and Gaza -- or at least a resolution of the Palestinian problem acceptable to Palestinians.
The Europeans do not expect this to emerge from the talks on Palestinian autonomy in which the Israelis and the Egyptians continue to be involved under Camp David.
One of the reasons for the skepticism of Europeans (and others) is that Mr. Begin and his hard-line Cabinet colleagues have made no secret of their long-term aim to annex the West Bank and Gaza. The Israelis interpret the Camp David accords as not precluding this.
(The Egyptians almost certainly share this skepticism but do not officially voice it lest it give the Israelis a pretext for not completing their withdrawal from Sinai in April.)
For the Israelis, it is one thing for the French to react positively to the Saudi plan but quite another -- and alarmingly so - for the US to be showing an interest in it. The US has the kind of clout that France has not.
Consequently one can understand how the warning lights must have flashed in Israel when a State Department spokesman in Washington referred on the morrow of the Senate AWACS vote in relatively favorable terms to the Saudi peace plan. The spokesman pointed out that the plan implicitly recognized Israel's right to exist. The US, he added, welcomed ''any contribution to achievement of a just and comprehensive peace in (the Middle East.)''
This, in Israeli eyes, raised the prospect of the US eventually agreeing to ''cut Camp David in half.'' In other words, the US -- once Israeli withdrawal from Sinai is completed -- might try to incorporate parts of the Saudi plan in a wider blueprint than that offered by Camp David for resolution of the outstanding Palestinian issue.
Even before the AWACS vote in the US Senate, former Israeli Ambassador to the US Simcha Dinitz was warning of just this in the columns of the Jerusalem Post.
If US efforts to involve Saudi Arabia in the political process in the Middle East succeed, he wrote, ''Israel will face, after the completion of its withdrawal (from Sinai), an American-Egyptian-Saudi policy which will be based not only on the Camp David agreements, but on their amplification through the addition of elements from the Saudi plan.''
In his Oct. 30 letter to Mr. Reagan, Mr. Begin argued that even if one of the eight points in the Saudi plan accepted by implication Saudi recognition of Israel as a state, the other seven would mean Israel's destruction.
Among these other seven are: Israeli evacuation of all Arab territories, including East Jerusalem, seized in the 1967 war; and the setting up of a Palestinian state with East Jerusalem as its capital.
These presumably are among the elements in the plan with which a US State Department spokesman said Oct. 30 ''we have problems.'' Mr. Begin clearly wants more than that kind of reservation from the US.