Asked to explain how President Carter won ratification of his controversial Panama Canal treaties in 1978, aides said that, in the end, their most effective argument was that Americans could not afford to have their president's international prestige demolished by a major foreign policy repudiation so early in his term. If Reagan manages to eke out a politically draining victory on AWACS, it will be because of the same argument.

From the beginning, AWACS threatened to become Reagan's Panama Canal:

* It was a foreign policy initiative with a strong and organized opposition and little passionate support. Yet it would require explicit congressional backing to become effective.

* The policy case was counterintuitive. Look at Reagan's trouble in explaining how selling advanced armaments to a regime that has opposed Camp David will advance regional peace and stability. So public support cannot easily be called in to buttress presidential lobbying.

* The proposed deal was bound to expose our negotiating partner to strong public attack in the United States. Critics would attack Saudi Arabia to strengthen their case for disapproval.

* Once the vote counts appeared unfavorable, AWACS would inevitably also expose Saudi Arabia--as the canal treaties did Panama--to senatorial pressures to improve the deal from the U.S. vantage point: to make explicit what was implicit, to convert private understandings to public commitments, to pin everything down legally and publicly in a form that would advertise Saudi weakness and dependence on the United States. Saudi unwillingness to play this American game was hardly surprising.

Thus the basic structure of Reagan's political problem was clear from the outset. A decision to go ahead was, in practice, a decision to take these risks and absorb these costs, to make AWACS a centerpiece of administration foreign policy both substantively and politically, and to shine a strong and critical spotlight on the Saudi connection.

Was it worth it? Almost certainly not, if it was avoidable, and there was an alternative approach--postponing AWACS but moving ahead with the F15 enhancement. This had far better political prospects because the Israeli government had reportedly acquiesced.

There is no evidence that the Reagan White House remotely understood what it was getting into before it made its spring AWACS commitment to the Saudis. Carter, by contrast, was well aware of the struggle he faced on Panama. The magnitude of the political problem was recognized early, and a broad, coordinated campaign was waged over a 15-month period to put it across. No comparable Reagan effort on AWACS was evident before September.

Our system makes it very hard for any administration to pursue subtle, nuanced policies relying on tacit rather than explicit understandings with other sovereign states. An administration gets more leeway with Congress if it seems to know what it is about on an issue--as Reagan's has not on AWACS.

But periodic congressional confrontations, "tests" of administration decisions and actions, are probably inevitable. They will tend to drain presidential capital. Therefore, any administration will need to limit the number of confrontations in which it engages--and be sure that each is really worth it.

In so doing, it will need to pay far greater heed than Reagan did to the "early warning system" built into current legislation on arms sales. Since 1974, Congress has had the authority to veto, by concurrent resolution, large non-NATO arms sales. It has yet to do so, but the threat of veto has altered the content of several proposals--including a 1977 Carter plan to sell AWACS to Iran and the 1978 "package deal" of aircraft sales to Saudi Arabia, Egypt and Israel.

On the AWACS sale to the Saudis, the early warning was loud and clear, but the Reagan administration was not listening. Its hearing aid should be turned up a bit higher in the future.

Given the costs of defeating AWACS, the Senate should reluctantly approve it. But the administration should not stumble blindly into a similar confrontation in the future.