Falling oil prices furrow brows from Dallas to Lagos. Good news for motorists is less so for indebted oil exporters, banks

In corporate suites throughout the United States -- and in government offices in Mexico City; Lagos, Nigeria; Caracas; and a dozen other capitals -- tumbling oil prices are being greeted with trepidation. Crude has plummeted in the past three days as a result of efforts by the Organization of Petroleum Exporting Countries (OPEC), which is desperate to secure its ``fair share'' of world oil sales.

The best of times for oil users looks like the worst of times for a dozen exporters and a score of American oil companies. The outlook, for instance, for a company such as Texaco, which is facing a dire legal challenge at the moment, is bleak. A Texas judge Tuesday upheld a $10.5 billion award against it and assessed an additional $600 million in interest.

Falling oil prices also put new strains on the international banking system.

In many ways, says a veteran oil industry observer, ``we are now in the day of the buyer.'' American motorists may see gasoline prices drop below $1 a gallon in the next few months if price cuts get passed along.

Kristin S. Lindow, an economist with the Wharton Middle East Economic Service in Washington, says $18 a barrel by late next year is plausible, but she adds that ``there is no logic for choosing a bottom.''

S. Fred Singer, a visiting professor at George Mason University and longtime OPEC analyst, says he thinks prices could drop to $10 to $15 a barrel, and that that would ``close down much of the production in the world.'' The aim, Dr. Singer says, would be for OPEC (meaning, effectively, Saudi Arabia) to extract promises of production cuts from non-OPEC countries such as Mexico, Britain, and Norway.

On Wednesday, the price of British North Sea crude fell below $22 a barrel, its lowest level in six years. It later recovered to around $24.50. Two weeks ago this oil went for more than $30 a barrel.

Each $1 drop should mean a 21/2-cent decline at the gasoline pump. As prices fall, consumption should pick up again -- but slowly. Economists say each 1 percent decline in prices leads to 0.1 percent greater demand.

Depending on how far prices drop, however, heavily indebted Mexico, Venezuela, and Nigeria could be in financial danger -- which also means problems for banks owed money by these countries.

Britain might have to forgo planned tax cuts.

Middle East oil producers would feel the pinch of lower prices. But those basically aligned with Saudi Arabia have the financial reserves to carry them through. The Saudis have some $100 billion to $150 billion in assets invested abroad.

In the ranks of multinational oil companies, those thathave transformed themselves primarily into buyers -- British Petroleum and Royal Dutch/Shell -- should continue to prosper.

Exxon and Mobil, which have diversified, should fare well, too. But heavily indebted companies such as Chevron and Texaco could be in trouble.

The most worrisome case is Texaco: Its problems in the Pennzoil court case may force it into bankruptcy. An appeal could still alter the damages or overturn the verdict. But even so, Texaco and other such oil companies have to cope with in-the-ground reserves becoming less and less valuable and sales revenue dwindling.

Oil-producing nations face a similar future. Of greatest concern is Mexico. A drop of only $2 to $3 a barrel would decrease Mexico's income by $4.6 billion by the end of 1986, notes Wharton Econometric Service in Philadelphia. A drop to $20 a barrel could wreak havoc with a nation trying to struggle out of $96.4 billion in debt and recover from the devastating earthquake three months ago.

At $20 a barrel, says William Cline, a senior fellow at the Institute for International Economics in Washington, Mexico's debt might have to be rescheduled, the peso devalued, and Washington might need to put together a special economic package to aid its southern neighbor.

On the other hand, a $6 drop in oil prices should result in a drop of 0.6 percent in the London Interbank rate, which determines the interest on Mexico's debt, Dr. Cline says.

This would save Mexico some $600 million. Lower oil prices would also stimulate growth in the US and Western Europe, thus allowing Mexico to sell more goods to these economies. These are offsetting factors -- but not enough to counterbalance the loss of oil revenue.

Venezuela, says Cline, does not have as large a debt burden ($35 billion) as Mexico, but its economy is not as diverse, either, so it would not be able to take advantage of the benefits of lower oil prices on economic growth elsewhere. He says Nigeria (which owes $20 billion) is ``very shaky already.'' Lower oil prices would hurt greatly and might force the country to speed up economic reforms.

In the US, lower oil prices would hurt not only oil companies but banks that have made energy-related loans. There are mitigating factors in oil states, too, however, since transportation and manufacturing costs would fall and disposable income should rise.

William Gibson, chief economist of Republic Bank in Dallas, says only 15 percent of Texas' economy depends on the oil industry. He says that while falling oil prices won't be good for Texas oil companies or banks, the ``benefits of lower prices would outweigh the negatives.''