ARAMCO quietly acknowledged this week that, sometime last spring, Saudi Arabia had completed the process of nationalizing it. That will have little effect on the daily operation of the world's oil industry. But the announcement draws attention to the extraordinary change in the role of the oil companies and the nature of their economic influence over the past decade.

Aramco, which comprises nearly the entire Saudi oil industry, is by far the world's largest oil producer. It was built a generation ago by four American companies -- first Texaco and Socal, later joined by Exxon and Mobil -- that now stay only as technical advisers. They will presumably continue to take most of the Saudis' oil exports -- but only as buyers, no longer as owners, of the oil.

The dominant position of the big international oil companies has been eroding steadily for 30 years. Before World War II, and for a few years after, the world oil trade was all but totaly controlled by seven of them. (In addition to the Aramco partners, they were Gulf Oil, British Petroleum and Royal Dutch Shell.) Countries that wanted to import or export had to deal through them.

Governments began to see advantages in putting more players into the game. At the time of the first oil crisis in 1973, all of the major oil companies together were producing 75 percent of all the oil that went into world trade. By last year, they were producing 42 percent of it. In 1973 the OPEC countries themselves were directly marketing 7 percent of their oil. Last year they were marketing 40 percent of it. Even those figures understate the control being exercised by the exporting countries. Not a pint of oil now crosses the border of any producing country except at volumes and prices set by its government.

The international oil companies continue to do an invaluable job as middlemen. They move oil from country to country with great efficiency, balancing supplies of dozens of grades and types against fluctuating needs. They do the technical work of finding and producing oil with immense skill. But they no longer control the production rates or the prices.

The oil companies have lost their market power, but they have gained great financial power. They did not arrange or even foresee the rapid run-up of prices over the past decade, but they have benefited hugely. Within the American economy there has been a great shift of wealth toward the oil industry. The profits flowing to the oil companies are, in effect, largely preempted from other enterprises.

When people speak of recycling oil surpluses, they generally mean finding ways to channel OPEC surpluses back to the oil-importing countries. But there's beginning to be a need for recycling within the American economy. There are limits, after all, to the amounts of money that oil companies can rationally spend drilling for more oil. One solution would be an increase in the modest oil windfall tax enacted earlier this year. But Congress does not seem likely to return to the subject soon. How are the increasingly rich oil companies to invest their funds without devouring other industries and permanently skewing American industrial competition?