The latest policy-making meeting of the Organization of Petroleum Exporting Countries ended in yet another deadlock today, with leading producers admitting that the group's price-fixing system, the foundation of its strength, existed in name only.

Speaking to journalists after the day-and-a-half OPEC session that adjourned today, Ahmed Zaki Yamani, the Saudi oil minister and the most powerful figure in the 13-nation cartel, admitted that even his nation had modified its position on OPEC's official pricing system.

"Well, I think there is a change now," Yamani said. "The last country that was following the official pricing system, Saudi Arabia, is changing, following the majority."

That decision, oil analysts here said, could mean a drop of between $3 and $4 for a barrel of oil by next spring, unless it triggers a price war among OPEC members that would result in a greater, and more unpredictable, drop.

Yamani's statement came after OPEC ministers had discussed Saudi Arabia's decision to peg some of its oil sales in the future to the market prices of its refined products rather than the long-defended OPEC-set benchmark price for a barrel of crude oil, which is currently $28.

Yamani said OPEC would have to begin talks on finding a new pricing system which, he said, is now a "de facto situation" in Saudi Arabia.

According to Subroto, the Indonesian minister of mines and energy who was unanimously reelected as the conference president, discussions on such a new pricing system will be starting immediately in a series of bilateral and multilateral talks among OPEC members between now and the organization's regular biannual meeting in Geneva on Dec. 6.

"We feel after 25 years of existence we are facing a new period in front of us, a new situation," Subroto said at a news conference at the end of the inconclusive special meeting. "We must devise a new action program, a new strategy, to deal with it."

Subroto said the much-discussed new pricing system, which has increasingly replaced the old as member nations broke ranks with the official price to try to make their oil more competitive through discounts and other schemes, would be part of the discussion of OPEC's new strategy for the future at the next meeting.

Yamani's statement on prices confirmed that the traditional OPEC order had broken down, even if he, as Subroto, continued to insist that the official price was still in effect, if only as a "guideline" for prices that are now influenced more by the market than OPEC decisions.

OPEC's oil production has shrunk from its 1979 high of 31 million barrels of oil a day to its current official ceiling of 16 million because of greater oil production by countries that do not belong to OPEC and oil conservation measures in consumer nations. As a result, discipline among OPEC members on both pricing and production has become increasingly weak or nonexistent.

That is a fact that Saudi Arabia, OPEC's largest producer and long its greatest proponent of united pricing, has finally had to admit by abandoning its reliance on official price rates. Ironically, Saudi Arabia's decision to follow the practices of the majority has drawn criticism from other OPEC nations who had relied on Saudi Arabia's determination to act as a swing producer to keep surpluses down and the price stable.

That role, however, had become increasingly intolerable for the Saudis as it was forced to decrease its production to 2 million barrels a day this summer, causing a $20 billion-a-year loss in the nation's foreign currency reserves.

Yamani repeatedly demanded that other OPEC nations adhere to OPEC production quotas and pricing because their failure to do so was harming Saudi Arabia's economy. When Saudi requests were ignored, Yamani this summer was instructed by King Fahd to begin the new market pricing with selected oil companies and to begin raising Saudi production toward its allotted 4.35 million-barrels-a-day quota.

Since August, when the decision to step up production was taken, Saudi Arabia has raised its production to more than 3 million barrels of oil a day, according to analysts here, and it is expected that by winter it will be pushing to meet its full quota.

Yamani today denied that this increase in production will affect prices adversely because oil demand has increased recently because of low western inventories, the approach of winter, disruptions of Soviet sales to Europe and Iran's inability to keep up a steady flow of oil to traditional buyers because of Iraqi bombing of its terminal at Kharg Island in the Persian Gulf.

"I don't expect prices to rise as a result of the Saudi Arabian action," Yamani insisted today. "Prices in fact are going up."

But Yamani said that might not be the case in the spring when world demand for OPEC oil can be expected to shrink again. He said he hoped that between now and February the question of a new pricing structure would be studied and acted upon. Along with the pricing issue, OPEC will also have to deal with the matter of reallocating oil quotas among member nations, the other key issue that this week's OPEC meeting chose, once again, to postpone.