The performance of Sen. Robert Packwood (R-Ore.) and his 50-or-so colleagues on the Saudi Arabian arms deal puts me in mind of that annual high school exercise when the students who think they know so much are allowed to run things, teach classes, rewrite the rules--just for a day.

It is heady stuff, and harmless. But playing foreign policy-maker by majority rule is something else. If Packwood & Co. have their way, a crucial component of the Reagan administration's grand strategy for the Middle East will have been wrecked beyond repair.

Part of this problem, surely, is the somewhat wild-eyed notion that a "strategic consensus" can be solidly built on the common anti-communist concerns of two mortal enemies. Saudi officials insist they can't afford to be saved by American forces working hand-in-glove with Israel--not while the embittering issue of Palestinian rights is unresolved.

For their part, the Israelis insist the Saudis can't be trusted with the five early-warning-and-command AWACS aircraft and the "enhancements" (fuel tanks, air-to-air missiles, tanker planes) for the 60 F15s whose sale the Congress has already sanctioned.

It's a tricky enough issue to cause Congress concern. But the way the Senate is approaching the issue raises real questions about the practical application of cherished congressional checks and balances to the making of coherent foreign policy.

The administration 's detailed, enormously complicated, highly technical proposal has not even reached the Capitol. No committee hearings have been held. Yet half of the world's self- proclaimed "greatest deliberative body" has completed its great deliberations and formally registered flat-out disapproval by cosponsoring a resolution of objection to the sale.

Now you can fault the administration for letting Israel and its supporters get off to such an early, overpowering start. And you cannot lightly dismiss their anger and anxieties. The Israelis, after all, fought against the F15s, and lost. They were clearly promised by the Carter administration there would be no "enhancements." When the Reagan administration went ahead anyway, the Israelis were first resistant and resentful, but finally reconciled.

Then came the AWACS, with their ultra-sophisticated computer consoles and data processors providing wide- ranging capability to detect enemy aircraft and control air battles by "vectoring" interceptors on their shortest course. It's a weapon you wouldn't want to have fall into hostile hands.

So there is something to the argument that Saudi Arabia is unstable; that the House of Saud or a radical successor might well make war on Israel, or somehow allow the AWACS to find their way to the Soviets.

But there is also much to be said, as well, for the administration's claim that the necessary safeguards are built in. Delivery of the first AWACS wouldn't be made until early 1986. Americans will continue to play an indispensable support role on the ground beyond the year 2000.

We are not, moreover, at square one. American-operated AWACS have been flying over Saudi Arabia and the Persian Gulf from Saudi bases since the outbreak of the Iraqi-Iranian war. The military argument, if it was sound to start with, seems no less sound to the Saudis now. The issue has to do with sovereignty and national pride.

American AWACS, in this sense, are no different from American bases or port facilities -- a return of the wicked "Western imperialists."

So against the risks of going ahead with the deal, you have to count, among the costs of canceling, the distinct possibility that the Saudis won't allow the American-operated AWACS to keep flying over Saudi Arabia.

You have to count, as well, the signal that this cancellation would send to even friendly Arabs. At recent Senate confirmation hearings, Sen. Charles McC. Mathias (R-Md.) questioned the ambassador-designates for Saudi Arabia, Yemen, Morocco, Syria and Algeria on just this point. "They all agreed," he reports "that the United States would be seen as unreliable and uninterested in dealing with the Arab world."

What is more, Israeli Prime Minister Menachem Begin would be seen as the manipulator of American Mideast policy. In some American circles, at least, he would be resented for having helped engineer the president's first congressional defeat--and a big one--on an international issue. Reagan's effectiveness would be undercut across the board.

The Saudis, for their part, would hardly be encouraged to go on playing what has been widely recognized as an exceedingly constructive backstage role with the Syrians and the PLO in the Lebanese missile crisis and the current cease-fire across the Israeli-Lebanese border.

Balancing all these risks and costs, in short, leaves the administration with a compelling case. The question is whether there are still enough senators sufficiently open-minded to hear it.