The latest round of oil prices increases shows a continuing decline in the power of Saudi Arabia. The country most sensitive to the interests of the United States and other advanced nations now finds itself almost isolated in the world of oil exporters.

The erosion of Saudi influence leaves a void that has been filled by random opportunism. In consequnce, while there is no immediate, overall shortage, the consumer countries find themselves ill-equipped to resist prices hikes.

Saudi Arabia, to be sure, remains an oil giant. It is producing 9.5 million barrels daily -- a substantial fraction of the 29 million barrels daily shipped by the OPEC cartel during the first quarter of this year. It has announced plans to expand capacity to 12 million barrels per day. It has by far the largest proved reserves of any country.

But the Saudis have little capacity for self-defense. Nor for organizing development of the kingdom with the vast sums acruing from oil sales. Nor even for managing the investment of those sums abroad.

The United States used to be the Saudi mainstay for production, development and investment. In return, this country was able to count on the Saudis to maintain relatively steady prices by expanding production.

Recently, however, the United States has looked increasingly unreliable. Inflation and the fall of the dollar have made this country less attractive as a storehouse for wealth. Iran underlined the inability of the U.S. to bring its military power directly to bear in the Persian Gulf. The American support of Israel exposes the Saudis to more and more pressure from other Arab countries, and the Palestinians, for a stronger stance against Washington.

Finally, there is the factor difficult to assess, but clearly important -- princely oil. The Saudis sell at least 7 million barrels daily under regular, long-term contracts to the four American oil companies (Exxon, Mobil, Texaco and Socal) grouped together as Aramco. Another million barrels a day or more are sold through various members of the royal family. They generally peddle the oil to buyers from other countries willing to pay commission above the regular price. The princes pocket the difference.

For all those reason, the Saudis have been less and less eager to be seen sticking their necks out to give the United States a good deal on price. If they are willing to move in that direction at all, they like to move in convoy -- as part of a general OPEC consensus.

Before the last OPEC meeting in Caracas in December, for example, the Saudis tried to organize a modest, general increase of $2 per barrel. Eventually they went far higher, when the African exporters -- Libya, Algeria and Nigeria, which produce the highest-quality oil from the sources closest to the United States and Europe -- held out for a stiffer increase. But for a while anyway, the Saudis held Venezuela and the Persian Gulf producers -- Iraq, Kuwait and the United Arab Emirates.

This month the Saudis tried the same maneuver. They raised the price of the basic crude that serves as a reference for all grades of petroleum from $26 to $28 per barrel. The hope was that other countries would sit still, and then join the Saudis in a generalized rise of $2 at the OPEC meeting set for Algiers beginning June 9.

This time nobody held. Venezuela and the Persian Gulf producers joined the African producers in matching the Saudi increase almost immediately. They are very likely to move the price, now averaging $30 per barrel, even higher (perhaps to about $2 per barrel) when they get together in Algeria next month.

At present there is no general oil shortage. Most countries hold ample stocks. Private companies working on a strictly commercial basis could perhaps drive down prices by refusing to take delivery at this time.

But among most consuming countries there is a general edginess about long-term supply. Iranian production, once more than 6 million barrels daily, is now below 1 million a day and could drop further. So much steam is out of the ayatollah's revolution that other Persian Gulf countries no longer feel the need to cooperate with the Saudis in order to isolate Iran. Indeed Iraq, Kuwait and the Emirates have recently curtailed production slightly, and may cut more deeply later.

Furthermore, there has recently taken place a dramatic shift of partners in the oil trade. Private companies, as recently as 1975, handled about 80 percent of the flow. Now the suppliers like to make country-to-country deals. pConsuming countries, nervous about future contracts if they bargan hard now, generally accept any price and even pay commissions. So still they can work out an effective strategy for dealing jointly with the exporters, the consuming countries will be apt to pay prices for which, as Energy Secretary Charles Duncan said in Paris the other day, "there is no economic justification."