Organization of Petroleum Exporting Countries ministers have raised a new set of warning flags with a familiar message for the rest of the world, following their weekend meeting in Geneva.

The message is that a price war lies ahead, next spring or summer, unless the other oil-exporters, the United States and the rest of the industrial world cooperate in stabilizing crude-oil production.

Analysts said a price war, driving crude-oil prices down below $20 a barrel from the current level of $28, would knock as much as 20 cents a gallon off gasoline and heating oil prices, benefiting consumers while battering the energy industry and oil-exporting nations. Each $1.00-a-barrel drop in prices for crude generally trims fuel product prices by about 2 1/2 cents a gallon.

The backlash from a price collapse would include a further contraction of the U.S. energy industry: More gasoline stations and refineries would be closed and more exploration projects would be shelved.

And it would mean a critical loss in oil revenue for Mexico, which is the second-biggest debtor among the developing countries. Mexico owes about $60 billion to commercial banks and another $35 billion to governments and official institutions. Oil finances nearly all of Mexico's imports and debt payments, and a financial crisis for Mexico would have wide repercussions.

But most observers don't believe the slide to $20 a barrel is a foregone conclusion. "It could happen, but I don't think it's at all certain," said John Lichtblau, head of Petroleum Industry Research Associates.

OPEC's most recent attempt to avoid such a self-inflicted wound was taken at a three-day conference in Geneva that ended yesterday.

The OPEC communique yesterday said that the ministers had agreed to joint action to defend a "fair share" of the world oil market. Industry experts said that means that OPEC is not willing to make a large enough cut in its production next spring to absorb all of the reduced demand for oil products when the winter heating season ends.

In the past, Saudi Arabia has taken up most of that seasonal production cutback, while most of the rest of OPEC and non-OPEC producers Britain and Norway essentially maintained production levels. The Saudis had announced that they no longer would play that role, and in Geneva they persuaded the rest of OPEC to join them in pressuring the non-OPEC producers.

"It's basically a warning to the non-OPEC producers not to push their luck," said Ted Eck, chief economist of Amoco Corp.

Analysts did not agree on the immediate impact of the weekend meeting, however.

Some, like Lichtblau, see OPEC's action giving a downward push to crude-oil prices, which have retreated recently from a $30-a-barrel level.

To others, the meeting produced no fundamental change. It "was basically a nonevent," said George Friesen of Dean Witter Reynolds Inc. The continuing inability of OPEC, which supplies one-third of the world's oil, to agree on production cutbacks has made future price reductions almost certain, and last weekend's meeting didn't change that outlook, Friesen said.

The moment of truth still lies ahead, in March or April, when the winter demand for heating oil suddenly drops, cutting demand for crude oil. And the question is, who will cut back, and by how much?

But the Saudis still may lead the way to a more gradual reduction that would stabilize prices in the $20- to $25-a-barrel level. OPEC "has pulled the rabbit out of the hat" at other times, he said.