A Senate staff study has concluded that failure to carry out President Reagan's proposed sale of radar planes to Saudi Arabia would damage U.S.-Saudi relations and could adversely affect U.S. plans for defense of the Persian Gulf region with its vital oil supplies.

The study also found that the sale is unlikely to pose a significant military threat to Israel. But it expressed concern about the danger of the Airborne Warning and Control System (AWACS) planes and another item in the $8.5 billion sales package, AIM9L air-to-air Sidewinder missiles, falling into the hands of the Soviets and providing Moscow with access to some of the most advanced equipment in the U.S. arsenal.

The study for the Foreign Relations Committee made no recommendations about whether the sale should be pursued. The thrust of its findings, however, as outlined in a summary made public yesterday, appeared to support the argument that U.S. interests would be served best if Saudi Arabia gets the AWACS under a revised agreement providing for U.S. participation in its operation.

The Reagan administration, fighting to prevent Congress from vetoing the sale, is trying to find a compromise capable of satisfying congressional calls for greater U.S. control and Saudi Arabia's sensitivities about infringement of its sovereignty.

In an interview yesterday with Edward Cody of The Washington Post, a high Saudi official and member of the ruling family said his government rejects any arrangement that would entail the obligatory presence of Americans in the AWACS crews beyond a necessary training period.

But, as two of President Reagan's strongest Senate supporters warned yesterday, the administration faces what one called "an awful lot of political bloodletting on the floor" of the Senate if it submits a sales package that does not include some form of joint crews and control.

The sale cannot proceed if both houses of Congress vote against it. An apparent irreversible majority against it exists in the House. In the Senate, where the administration has pinned its hopes for victory, the expectation is that a majority will vote to veto the deal unless the president can win Saudi agreement to greater U.S. control over the AWACS.

The "bloodletting" warning was issued by Sen. Paul Laxalt (R-Nev.), Reagan's closest friend in the Senate. But Laxalt, who was interviewed on the television news show "Meet the Press" (NBC, WRC), said the sale had "an excellent" chance if it is modified to meet Senate concerns.

Sen. John G. Tower (R-Tex.), chairman of the Armed Services Committee which will begin hearings on the sale today, said on the Cable News Network that he strongly supports the sales package in its present form but added "it is quite obvious the Senate wants all of the assurances from the Saudis it can get."

The Foreign Relations Committee report was prepared by four professional staff members: Hans Binnendijk, George W. Ashworth, Robert Bell and Michael Kraft. In releasing the summary yesterday, the committee chairman, Sen. Charles H. Percy (R-Ill.), said copies of the classified study had been distributed to committee members and an unclassified version probably will be made public later this week.

As described in the summary, the study found that disapproval of the sale would set back U.S. efforts to cultivate close ties with the Saudis. It said the adverse consequences probably would not be abrupt nor manifested in Saudi oil production and sales policy but would be felt more in Saudi unwillingness to assist the Mideast peace process and in a lessening of U.S.-Saudi trade.

Regarding U.S. strategy in the Persian Gulf, the study said, "U.S. access to Saudi Arabia would be crucial in time of war if the United States were to attempt to defend Iran from Soviet attack." In that respect, it added, the sale would enhance Saudi willingness to allow U.S. use of bases within its territory and a sharing of U.S.-made equipment in Saudi possession.

On the security question, the study said capture of an AWACS or an AIM9L "remains high on the list of Soviet intelligence targets," and "stringent security measures will be required if the sale is approved."

Discussing the potential threat to Israel, the report found that Saudi attempts to use the equipment against Israel would involve costs and problems that would make the Saudis hesitant. It said, "As a result, a Saudi AWACS would not significantly alter the current Arab-Israeli air balance."