WHAT OPEC decided, or didn't decide, at its OPEC meeting makes little difference. Everything now depends on Saudi Arabia and its enormous oil production.

Since OPEC apparently couldn't agree on anything else, it amicably agreed to continue the present disagreement among its 13 member governments. Or ws it entirely amicable? Tensions among the 13 members are running high. The recent stability, and slight decline, in oil prices is solely the result of a deliberate Saudi policy to overproduce and create a worldwide oil surplus.

While OPEC is frequently called a cartel, it cannot impose prices on its memb ers nor has it ever attempted to tell any of them how much to produce. It does not control access to the market. Its decisions do little more than pretend to ratify the realities of prices being set in the world market by supply and demand. It's the supply decisions by the exporting governments that will determine prices in the weeks ahead, and by far the biggest of the exporters is Saudi Arabia.

The Saudis went to Geneva offering the rest of OPEC a deal. They would raise their relatively low price of $32 a barrel if the high flyers -- Libya, Algeria, Nigeria--would come down under $40 and submit to a unified OPEC price schedule. But the deal collapsed in the usual conflicts of national pride and national interest.

The Saudis' ultimate purposes are a matter of speculation. One motive is evidently a matter of sheer national precedence--establishing the principle that Saudi Arabia, as the greatest by far of the oil exporters, ought to dominate the price structure. Presumably another motive is to keep reminding Europeans and particularly Americans that Saudi Arabia is the brake on the North African radicals, whose lust for still higher prices knows no bounds. The Saudi government likes the western countries to keep thinking about their interest in its perpetuation in power.

Whatever the full range of the Saudis reasons for the present overproduction, it would be dangerously wrong to suppose that they could not cut their exports quickly and sharply if they chose. They are currently earning far higher avenues, than they need. At any time they could cut their spending merely by canceling construction projects that they need only marginally if at all.

Much economic analysis these days confidently predicts that oil prices will remain stable in the months ahead. That's quite true, as long as (1) the Saudi government doesn't change its mind, or change hands, or (2) the Iran-Iraq war doesn't suddenly wake up, or (3) there are no other nasty surprises in the Middle East or anywhere else to disrupt the flow of oil. It is possible, theoretically, that the world is now moving into a halcyon time when, unlike the 1970s, there will be no more nasty surprises. But in view of recent experience no sensible American consumer, or prudent American government, will bet on it.