Saudi Arabia, confronting a severe budget crisis caused by plunging oil revenues, is demanding that its OPEC partners accept a new quota system that would enable Riyadh to begin producing more oil as soon as possible.

According to well-placed delegates, the ultimatum by the world's richest oil producer was presented today by Saudi Oil Minister Ahmed Zaki Yamani, who told fellow ministers at a critical meeting of the 13-nation Organization of Petroleum Exporting Countries that the desert kingdom no longer could accept its role as the "swing producer" that adjusts its output to support prices fixed by the cartel.

Saudi oil output has dwindled to a 20-year low of 2.3 million barrels a day, less than that of Britain, in an attempt to shore up sliding prices in a world of surplus oil. But the drastic cuts have failed to prop up the market, and the Saudis now want to assume a fixed production quota along with other OPEC members.

OPEC prices are pegged to the official $28 a barrel benchmark price for Saudi light crude.

In recent weeks Yamani and King Fahd have indicated that Saudi Arabia is prepared to raise its production as much as 2 million barrels a day unless cooperation is forthcoming from other OPEC members. Some analysts predict that such a move in an era of surplus oil could drive prices as low as $20 a barrel.

The Saudis favor a "floating" level of OPEC production, which would fall during the northern summer, when fuel oil sales taper off, and rise during winter or periods of peak consumption. Because of Saudi restraint, OPEC is now pumping only 14.5 million barrels a day, well below its self-imposed ceiling of 16 million barrels. The "floating" quota plan would link the cartel more firmly with market forces, the conference sources said.

Earlier, the ministers discussed creating a new central body that would "control the marketing" of OPEC oil, according to the ministerial conference chairman, Indonesian Oil Minister Subroto. By coordinating the sale of OPEC oil, the new agency would, in theory, monitor prices and production and thus make it more difficult for members to "cheat" by making hidden discounts or barter arrangements.

But Saudi Arabia, among other members, expressed skepticism about such an agency because it would take too long to organize and inevitably would face problems about national sovereignty over oil supplies.

Following an afternoon session, Subroto said the ministers decided to set aside the establishment of a marketing body as a long-term project. When they resume discussions Sunday, the ministers will "seek some immediate measures to defend OPEC prices and its share of the market," Subroto said.

Alluding to the recent history of members who have undercut prices or churned out oil surpassing their individual quotas, Subroto said, "We have begun to discuss practices that are weakening the market." But he indicated that OPEC was no nearer to solving its problems when he said the ministers "were asked to come with suggestions about what to do in the short term to defend our prices" when they reconvene Sunday morning.

Once more, the focus of attention at the OPEC meetings has centered on Saudi Arabia's Yamani, who has warned recently that his country cannot go on for much longer at such low levels of oil production when other OPEC members are undermining the cartel's strategy.

Some analysts contend that Yamani is maneuvering the cartel toward a reduced price structure, more attuned to slack world demand, by letting pressure build on his colleagues and spreading the message that Saudi oil production will rise soon no matter what the others do.

Yamani skipped the morning session today, saying he was ill. But many observers perceived his absence as a diplomatic rebuff to those who wanted to talk about the new marketing agency as a cure for OPEC's woes.

In the afternoon, the Saudi minister guided discussion about the "floating ceiling" concept, which would tailor OPEC oil outputs to the needs of the market. The notion seemed compatible with the arguments of those members who believe OPEC's only recourse is to slash oil output even more to soak up the glut on the market.

Representatives from Libya and Algeria, who have objected vigorously to Yamani's previous hints about possible price cuts, have been the leading advocates of a steep decline in production. But several hard-pressed OPEC members such as Nigeria, Venezuela and Indonesia insist that they cannot trim back any more because they would risk default on massive debts.

In the absence of any consensus about what to do to bolster sagging oil prices, the OPEC ministers have refrained from declaring their gathering a "formal session" in which they would make decisions and instead have characterized their two days of talks here as "consultations."

The OPEC members clearly are troubled by the prospects that inconclusive results at their weekend meeting here will send negative signals to the market when it reopens Monday and probably lead to a further erosion in oil prices.

Some delegates have hinted that the consultations may be called off by Monday, with a formal conference to be scheduled again later this month to give OPEC members more time to figure out ways to regain control of the slumping oil market. Such a decision would be consistent with the cartel's pattern of muddling through its crisis in the hope that world economic recovery will yield an upturn in oil demand.

The ministers appear to have avoided any consideration so far of a general price cut that would bring OPEC rates more in line with prices on the free or "spot" market, where as much as 80 percent of the world's oil is now changing hands at prices $2 to $4 below OPEC levels.