THE OIL-EXPORTING countries are now demonstrating that, even in the midst of a slight glut, they still have the power to keep raising their prices. First the Saudis went up $2 a barrel. Now most of the others are following them by the same $2 a barrel. Next month, as the cycle is completed, the cost of oil coming into this country will average about $35 a barrel. Seven years ago, just before the first oil crisis, the same kind of oil was being unloaded at Houston at $3.25 a barrel.

The immediate victim of this latest increase is the theory that, as long as storage tanks were brimming all over the world, the producers would never be able to raise prices. April is, after all, the slackest of slack times in the oil markets; the winter is over, and the vacation season with its surge in gasoline sales hasn't yet begun. But this year April came and went without any signs of softening in the market. To the contrary, spot prices inched up a little. The Saudis saw that they had an opportunity, and took it.

Why do oil companies keep paying more for oil, even when their stocks are high and sales are slowing down? The answer is that they are fearful of being cut off from their foreign sources in the next emergency. As they see it, they are investing in good relations with exporting governments. They pay this month's price increase quickly and without protest, in hopes of buying an opportunity to be at the front of the line to buy again during the shortage that might develop next month, or next year. Stocks this year are large compared with last year, but small compared with the world's inordinate daily requirements. The normal economics of supply and demand is being skewed by a widespread anticipation that eventually, probably sooner rather than later, there will be another squeeze on the oil line.

After the first oil crisis in 1973-74, prices shot up but rapidly hit a plateau. They remained stable for the next four years. In real terms, adjusted for inflation, oil prices -- and gasoline prices here in the United States -- actually fell between 1974 and 1978. The OPEC countries are acutely aware that they lost ground to inflation in those years. The current increases are a broad hint that there is not going to be any similar respite for the customers after the 1979 oil crisis.

The United States has reduced its imports sharply over the past year -- by more than a million barrels a day. But world oil production is also down. It's not just revolutionary Iran. For various reasons, Kuwait, Venezuela, Nigeria and Algeria have all reduced oil exports within the past year. The downward trend is likely to continue.

If the industrial countries really want to stabilize the price of oil, they are going to have to push their imports down harder and faster to create real slack in the market. Reducing oil imports will once again be the most urgent business confronting the world's seven major industrial nations next month, when the heads of their governments meet in Venice. There, if the hotels give them good rooms, they will get constant reminders of that reality as they see the procession of tankers plowing heavily through the lagoon on their way to the modern oil port that lies behind the medieval city.