As Congress nears consideration of the Reagan administration's approval of the sale of advanced radar planes to Saudi Arabia, two Mideast developments are giving the Saudi argument a boost:
* Apparent softening of Israeli opposition to the AWACS (airborne warning and control systems) deal.
* The new threat to Saudi Arabia and other conservative Arab states posed by the alliance of pro-Soviet South Yemen, Ethiopia, and Libya.
Also aiding the Saudis' cause was continued moderation on oil prices at the rec ent Geneva oil summit. Diplomats in the Mideast say this serves to "sweeten the pot" in Congress running up to the Oct. 30 deadline for vetoing President Reagan's decision to sell Saudi Arabia five AWACS (airborne warning and control systems) planes.
The most widely acknowledged stumbling block to congressional approval, however, has been Israel, which exerts considerable influence in Congress. But the tone of a recent policy statement by Israeli Foreign Minister Yitzhak Shamir indicates the top levels of the Menachem Begin government may be deemphasizing the alleged danger the AWACS constitute in the hands of Saudi Arabia.
On Sept. 1, in an interview with a correspondent for Israeli radio, Mr. Shamir was asked why he was not campaigning actively against the AWACS deal with leaders of the American Jewish Community who were in Israel at the time.
"We have many other problems," Mr. Shamir replied. He added that he and Prime Minister Begin would continue to lobby against the AWACS sale when they meet with President Reagan in Washington next week, but "everyone knows that Israel opposes this giving of sophisticated arms to Saudi Arabia or any other Arab state, and we consider it a grave danger to our security."
This relatively low-keyed approach -- when contrasted with the dire warnings from Israel since the AWACS deal was mooted last year -- meshes with the analyses of Western diplomats who have said that while the Israeli government publicly opposes AWACS for the Saudis, it will not be too upset if the sale goes through.
Western, Israeli, and Arab political analysts see this as part of a deal -- firmly denied by Israel -- involving AWACS approval in exchange for unhindered delivery of US warplanes to Israel. Other elements include guarantees by the US that the AWACS will be under American supervision and will not be used to spy on Israel. Also mentioned is possible Israeli access to information from US spy satellites over the Mideast.
Diplomats in Israel have pointed out that because the Begin government propounds the theory that Soviet influence, not the unsettled Palestinian question, is the main cause of instability in the Middle East, AWACS in Saudi Arabia would naturally follow. AWACS, one diplomat observes, are meant to protect a state's borders from Afghanistan-like invasion; the Palestinian problem is more of a localized problem for Saudi Arabia.
But the greatest boon to the Saudi cause appeared Aug. 19 with the sealing of an alliance of South Yemen, Ethiopia, and Libya.Stated goal of the alliance is the countering of Western influence in the Arab world, the Horn of Africa, and the Indian Ocean.
The alliance spotlights East-West polarization in the Red Sea region, which several Arab-watchers have said may soon eclipse the Gulf as a crisis area: Besides proximity to the Suez Canal, the Red Sea region is becoming increasingly important to the West due to the new Saudi oil terminal at Yanbu, through which 1.2 million barrels of oil per day are to be pumped by the end of the year.
Riyadh has long been concerned about Marxist South Yemen. Linkup of South Yemen and Ethiopia gives the pro-Soviet states control of the southern straits of the Red Sea. The Libyan connection adds money to finance what treaty signatories have proclaimed as their goal: "liberation of the Arabian Peninsula, " two-thirds of which is Saudi Arabian.
At the summit, Col. Muammar Qaddafi Specifically attacked "those who bend beefore the US and who are on the border of South Yemen" and "those who own dollars and live in palaces." The alliance's first step, Colonel Qaddafi said Aug. 25 in Damascus, will be to help South Yemen "unite with North Yemen . . . the beginning of the attainment of the Arabian Peninsula's unity."
The next step, according to a longtime Mideast watcher who subscribes to a kind of Red Sea "domino theory," would be subversion of Sudan, then Egypt and Saudi Arabia.