London — With OPEC looking in more and more disarray, conventional wisdom in world capitals is that if oil prices dropped to as little as $20 a barrel, producers would be hurt, the banking system would be strained, and consumers would be helped.
Within that broad framework, however, are a number of complexities and nuances now receiving close study in many a foreign ministry and energy boardroom.
* While the oil-consuming industrial world will be helped out of recession by cheaper energy costs, the search for other types of energy, already slowing, will lose even more momentum.
Development of expensive new North Sea fields is already stagnant. Work in the Beaufort Sea (Canadian Arctic) would slow. The French will have less incentive to keep on spending large sums on their nuclear power-generating plants. Large existing Japanese investment in liquefied natural gas (LNG) tankers would become much less economic. So would such projects as the new trans-Mediterranean, 2,500-kilometer gas pipeline between Algeria and Italy.
* Dependence on oil will rise.
''In 10 to 15 years,'' says one leading British oil economist, ''you could see a new energy crisis: too many countries needing oil and the price going up again. . . .''
In so saying he found himself agreeing with leaders of the Organization of Petroleum Exporting Countries, who continually warn the Western world that a dramatic drop in prices means higher consumer demand and higher prices in the 1990s. This is also the view of the International Energy Agency in Paris, set up by major industrial nations to orchestrate a campaign to move away from imported oil.
* Falling revenues could bring political instability.
Analysts and economists agreed in interviews that political instability could arise in oil-producing nations, and in its very violence and unpredictability hurt oil supplies and help push prices back up again. They focus on Nigeria and Iran in particular.
Nigeria, facing elections later this year, has already expelled upward of 1 million alien workers and faces a population restless at having to accept lower expectations.
''I wouldn't be surprised at another military takeover there,'' says one oil economist.
As for Iran, it is heavily dependent on oil revenues, and has a record of acting in ways the West finds difficult to predict or understand. A number of analysts here, noting Iran's anger with Saudi Arabia over aid to Iraq, worry that Ayatollah Khomeini or his aides might be tempted to close the Strait of Hormuz, imperiling oil supplies to Western Europe and Japan.
The big losers would be oil producers with big and poor populations: Nigeria, Venezuela, Algeria, Iran, Mexico. These would suffer a much worse loss of income , more indebtedness, lower standards of living, possible political repercussions and coups.
Less hard-hit, but also suffering, would be big oil earners with smaller, less demanding populations: Saudi Arabia, Kuwait, the United Arab Emirates.
Each country must watch the exchange rate of its own currency against the dollar, since oil is bought and sold in dollars. If the dollar strengthens, oil becomes even more expensive - and the dollar might well appreciate on exchange markets if lower oil prices boost the American economy out of recession, economists agree.
''On the other hand,'' says one political economist here, ''a pickup of economic activity in the US will mean a flood of imports over exports, and thus a trade imbalance. That in turn will weaken the dollar, and many another country will benefit from that.''
As for the world banking system facing huge unpaid loans in Mexico, Venezuela , Nigeria and elsewhere, much depends on how quickly oil prices fall, and by how much the fall stimulates world economic growth, thus boosting general non-oil trade.
Countries like Britain, which are self-sufficient in oil, will lose revenue in government taxes, but will gain from a surge of world economic demand.
Looking at the impact of cheaper oil on other countries, analysts see different scenarios.
France will find it harder to contain its commitment to nuclear energy, which now accounts for about 30 percent of all electrical power generated.
Britain will engage in less additional development of North Sea oil fields. Production costs in newer fields are close to $20 a barrel. Also, the government will receive revenue - but that could be offset by a higher gasoline tax after the next election here.
Canada will have less incentive to develop the Beaufort Sea region in the Arctic, or the oil sands in Alberta.
Japan will welcome a reduction in energy costs, but have less incentive to keep on with liquified natural gas (LNG) tankers.
Italy will have less need to buy Algerian gas. The new Mediterranean pipepline, completed in 1981, has lain empty while Algiers and Rome haggled over the price. Cheaper oil will mean the price will have to be renegotiated yet again - downward, making the line less economical.