OIL IMPORTS into the United States this summer have been running one-fourth below last summer's level -- an astonishing decline in so short a time. Part of it is due to the Recession. Part is due to the end of the frantic stockpiling and tankfilling that went on after the spring shortages last year. Part of the decline -- a small part -- is due to a slight increase in American oil production. But most of it is the result of conservation, enforced by higher prices.

That's good. It means that the trends in oil consumption and imports will continue downward, because prices will certainly keep rising. It's not only that drivers are using less gasoline. Over the first seven months of this year, consumption of home heating oil fell even faster than gasoline. A lot of homeowners switched to natural gas. A lot more simply kept their houses a little cooler -- and perhaps caulked their windows.

The savings in industrial fuel have been especially striking. After the 1973-74 Arab embargo, and the first round of price increases, industrial fuel demand dropped sharply. At the time, some authorities on the subject felt that the swing to conservation couldn't last. They said that the first steps were always the easy ones -- wrapping pipes, turning off lights -- and couldn't be repeated. But there were engineers who argued that in fact the really impressive savings would come in the longer run as companies began replacing their capital equipment with new machines designed for an era of very expensive energy. That turns out to be right. In American industry there has been a steady drop in the ratio of energy input to productive output.

American imports have now sunk close to the rate at the trough of the last recession in 1975 -- when there were some 20 million fewer cars and trucks on the highways, and industrial production was 25 percent lower than it is now. But in the recovery from the last recession, the price controls oil kept it relatively cheap, and the country used far too much of it. Imports shot up, putting enormous pressure on the entire world market. When the Iranian revolution shut down one important source of supply, the price took off again.

As it comes out of the present recession next year, the United States will have an opportunity to do the reverse. It can restrain prices by continuing to cut down the volume of oil that it imports. The American economy is turning out to be far more resilient, far more flexible and far more responsive to price changes than almost anyone thought possible five years ago. Decontrolling oil prices will stand as President Carter's most important and most courageous contribution, over the past four years, to energy policy and future economic stability.