Does Saudi Arabia help America out of good will or self-interest? An endless public debate rages around that question for a very good reason -- namely, that it is unanswerable. But the fact is that the Saudis do aid this country, and at some risk to themselves. So it is important to think hard about how the United States can best deal cards to the Saudi leadership.

Saudi support for American objectives finds current expression in two important areas -- the price of oil and the effort to ease tension in the Middle East. Each case underlines the impossibility of determining motive.

As regards oil, the Saudis are keeping production high (10.5 million barrrels daily, or 40 percent of the total output of the OPEC cartel) and prices low ($32 a barrel for the same crude others are selling for more than $36). The Saudis could easily increase their price by $4 a barrel, and reap greater rewards.

But do they forgo the increase because they want to help the industrialized world, or to maximize their power as the swing producer inside OPEC? Nobody knows, or can know. What is clear is that the United States and its chief allies benefit from Saudi policy.

As to easing tensions, the Saudis play a central role in the effort of Ambassador Philip Habib to defuse the row between Israel and Syria over Lebanon. King Khalid sent his brother, Abdullah, to Damascus, and President Hafez Assad sent his brother, Rifat Assad, to Riyadh. Presumably, the Saudis have offered to raise subsidies to Damascus, if the Syrians thin out their presence in Lebanon, which triggered the crisis with Israel.

But do the Saudis play that role to oblige the United States, or to avoid instability harmful to their own security? Once again, nobody can tell. But clearly the United States, among others, benefits.

The risks being taken by the Saudis, while less plain, cannot be doubted. The kingdom is ruled by a royal family working within the context of a puritanical religious sect. Economic dynamism, technological advance and the presence of foreigners all work to sap authority. The more so as the native labor force is insufficient in both size and skills. A going Saudi economy depends on large numbers of immigrant workers -- Palestinians, Egyptians, Syrians, Yemenis, Pakistanis and Indians. These outsiders are dry leaves ready for burning.

The help the United States can bring to the Saudis chiefly lies in the domain of strengthening the royal regime against its enemies. A first, obvious bit of assistance is to offset the threat posed by the Soviet Union and its various allies. That not only means stationing American forces nearby and providing intelligence data. Much more important, it means putting pressure on the radical regimes that act as Soviet proxies in the area. It is particularly useful to the Saudis for the United States to make life harder for the Libyans, the South Yemenis and the Cubans.

A second obvious service the United States can render the Saudis lies in energy conservation here in this country. Saudi influence inside OPEC diminishes when the market is tight. Then the hawks (notably Libya, Algeria, Nigeria, Iran and, most recently, Iraq) can force the bidding upward. By holding down consumption, the United States reinforces the Saudis' strength inside OPEC, and reduces pressures other countries can bring to bear on Riyadh. In that connection, by far the most important American contribution -- and the chief condition behind the current oil surplus -- is the growing trend toward fuel-efficient automobiles.

A third card the Americans can deal to the Saudis involves the Palestinian cause. The Saudis become particularly vulnerable to outside pressures when they sustain Americans who are then perceived to be standing adamantly in the way of Palestinian interests. So the United States helps the Saudis when it acts to promote some movement toward some realization of Palestinian objectives. But the emphasis is on "some movement" and "some realization." Going all out for the creation of a Palestinian state not only subverts the existence of Israel; it also works against President Sadat of Egypt, who is keyed to peace with the Israelis. It thus threatens the stability of the Mideast, as a whole, and particularly royal rule in Jordan and Saudi Arabia.

So accommodation of this country's various interests in the Mideast does not lie beyond the wit of man. The United States can maintain good relations with Israel and Egypt and Saudi Arabia. What is required is putting intellectual effort into discriminating choices -- which is different from wasting it on fruitless debate on Saudi motives.