These days the face of the oil importing world is set in a mask of fear.

Japan has more than 100 days' stocks on hand. Every Japanese tank and tanker is full, but Japanese companies still search for storage space in other countries, and government officials make strident speeches about the need to supplant the United States commercially in the Persian Gulf to ensure the future flow of oil.

A fear of being caught short has overcome all other considerations.

Oil buyers from Japan and elsewhere swarm to Iran and other countries where oil is to be had that is not sold directly to the international oil giants. Those same giant companies, of course, are cutting off all their contracts for delivery of crude because they need whatever they can get for their own refineries.

Great Britain swiftly raises the price of North Sea oil to levels matching the highest within the Organization of Petroleum Exporting Countries, and then, remembering all too clearly the recent days when it wasn't an oil exporter, announces plans to curtail production to extend its oil self-sufficiency to the end of the century instead of the end of the decade.

West Germany complains bitterly about continued high U.S. oil imports while seeing to it that oil companies operating there buy on the spot market to keep Germany's storage tanks brimming. And though still proclaiming the virtues of his nation's lack of price controls on oil products, in contrast with the situation in the United States, Chancellor Helmut Schmidt launches sharp attacks on oil companies profits reminiscent of President Carter's.

In this scramble, the fear of future shortage easily has outweighed any reluctance to pay astronomical prices, especially on the spot market where they top $40.

Over the course of 1979, the details of this picture of a world market dominated by fear changed from month to month, but the overal image did not. OPEC, of course, took full advantage of the chaos.

At the end of 1978, the average price of crude oil outside the United States was barely over $13 a barrel. Now it is approaching $30 as sellers leapfrog one another's price increases, and the total OPEC take is close to $900 million a day.

In the United States, the price at the pump for most grades of gasoline is wel beyond $1 a gallon, and the price of home heating oil is nearly 90 cents a gallon -- and already beyond it in the Washington area.

In 1980, the bill for imported oil will be close to $50 billion more than it was in 1978. That's bigger than the incredible increase in oil prices at the end of 1973.

So it's not surprising -- even though many people seem to find it hard to believe -- that Americans are using less oil than they did.

In 1978 American business and consumers used an average of 18.8 million barrels of petroleum products a day. Last year, a combination of slow economic growth, switches to other fuels, sharply higher prices and gasoline lines from May to July in some parts of the country cut that to 18.4 million.

A recession, more fuel switching, still higher prices and a new surge in conservation awareness should cut that to no more than 18 million barrels a day, and perhaps less, this year.

Net oil imports reached a peak of just over 8.5 million barrels in 1977. The following year, as production from the North Slope of Alaska picked up, net imports dropped to 7.8 million barrels a day despite higher consumption. In 1979 net imports fell to 7.6 million barrels a day, which included a substantial increase in stocks of oil.

This year imports probably will be no more than 7.2 million barrels a dsy and conceivably could fall all the way to 7 million. They haven't been that low since 1975.

Thus, it is clear that efforts to trim the U.S. appetite for oil are gaining ground.

Industry, perhaps more sensitive to energy price changes than consumers, has reduced sharply its consumption of energy per unit of output. Automobile efficiencies are climbing rapidly under legislative mandate, and because of the higher prices for gasoline, the average car is being driven fewer miles. And nearly 200,000 homeowners and numerous apartment building owners switched form oil to natural gas for heating last year.Aided by special tax breaks, thousands more were adding insulation, putting up storm windows and caulking drafty cracks.

Efforts to produce more energy are proceeding apace, too.

About 48,000 new oil and gas wells were drilled during 1979 even though exploration activity was slowed by questions about how the Natural Gas Policy Act passed late in 1977 would be implemented. Strikes are being made, but generally not enough to halt the long-term decline in production of either gas or oil but certainly enough to slow that drop.

Oil from new fields can be sold for the full market price today. The prices of oil from older fileds is being decontrolled, with about 2.5 percent of total U.S. production being freed each month. As domestic crude prices rise, so will prices at the pump -- probably by an additional 10 cents to 15 cents a gallon this year as a result of decontrol alone.

But by October of next year, controls on crude oil and petroleum product prices should be a thing of the past. Even bitter election-year complaints about oil company profits, which will be at record levels in 1980, are not likely to change that fact.

And as U.S. oil prices begin fully to reflect reality, encouraging conservation even as they hurt economically, other major energy issues are nearing some resolution:

Windfall tax. President Carter's proposed tax to recapture part of the "windfall" to il producers from decontrol has passed both the House and Senate, but in different form. Just before Christmas, conferees on the bill agreed to split the difference so that the levy, which will be in the form of an excise tax on crude oil, will raise $227 billion between now and 1990. Raising that much revenue will require taxing newly discovered oil more heavily than the Senate wished or reducing the exemption it allowed independents who produce less than 1,000 barrels a day.

Synthetic fuels. The $88 billion carter proposal to create a government corporation to oversee development of synthetic fuels, such as liquids from coal, oil from shale, or "natural" gas from coal, also has passed both houses of Congress, albeit in much reduced form. The conferees have agreed on the corporation form and the size of the programs: $20 billion. But many other points remain to be resolved, including what to do with another $14 billion worth of support n the Senate version for gasohol, solar energy and various energy conservation efforts.

Energy mobilization board. This third Carter proposal, now before a House-Senate conference, would create a board to speed siting and construction of energy projects such as new oil refineries or power plants. The conferees are sharply divided over how much power the board should have, particularly whether it could waive any substantive provisons of environmental law.

All three of these measures should pass in a form President Carter will accept some time early this year. Meanwhile, the administration is puting the final touches on a standby gasoline-rationing plan to submit for congressional approval.

But Carter said recently he wants authority to implement the plan, or some version of it, when a shortage reaches only 5 percent of consumption, not 20 percent, as the present law provides. That is sure to provoke another bitter rationing debate this year.

And Carter aides are braced for an all-out battle with electric utilities over provisions of a law Carter soon will propose requiring the utilities to switch from oil to coal as fast as they can while providing them tax credits or outright grants to assist the process.

Meanwhile, administration officials still are mulling whether it would be a good idea to try to effect another big cut in gasoline consumption through a major increase n the 4-cent-a-gallon federal gasoline tax, through imposition of an import fee on crude oil of $3 or $4 a barrel (a barrel holds 42 gallons), or through some milder form of gasoline rationing.

After looking closely at all three last month, administration officials didn't reach a consensus -- one wasn't even approached, some involved officials said. Now any such proposal won't come until March, at the earliest, when the Untied States meets again with the other member nations of the International Energy Agency to try to reach agreement on limits on oil imports for 1980.

In March, with the end of the winter heating season approaching, many energy experts believe oil will be readily available on world markets, and spot prices will be falling back to "official" levels. Some OPEC producers then may cut production as demand slackens.

But even then, the fear that has driven world oil markets for the past year still will be present. Iran still will be an uncertain supplier even if nothing happens in the next two or three months to halt its oil production. Saudi Arabian production intentions remain unclear from quarter to quarter.

There is a limit, however, to how much the oil importers of the world can do to protect themselves against a supply interruption. There are only so many oil tanks and tankers in the world to be filled.