THE PROPER RESPONSE to the approaching oil shortage is a gasoline tax of 50 cents a gallon -- half of it imposed immediately, half in September. A cut in income taxes could keep the total tax burden from rising, while shifting it heavily onto people who drive. A price of $1.15 a gallon would constitute a signal of the clearest and most comprehensible kind to American motorists to cut down gasoline consumption, in the national interest and their own.

We do not really suppose that the government is likely to raise gasoline taxes. Our purpose in making the proposal is only to remind readers that the United States is not destitute of the means to protect itself from the worst consequences of a shortage. If it does not use them, it is only because they are inconvenient and unpopular.

President Carter grappled with this dilemma once again at his press conference Monday. He wants Americans to conserve oil, but he doesn't want to start a scare or encourage hoarding. He said that, yes, the situation is serious but, no, it isn't a crisis. But then again, things could certainly get worse, in which case "we would have to take more strenuous action." Mr. Carter's cautious and tangled explanations do not greatly help other citizens to understand the present necessities. Nor is it useful for Mr. Carter to keep saying that, even before the Iranian revolution, imports from Iran were only about 2.5 percent of this country's total oil supply. What about Japan, which got one fifth of its oil from Iran and has hardly any other source of energy than imported oil? What about Germany, whose largest supplier was Iran?

As consumers abroad begin to run short, they will naturally begin to bid against American buyers. Prices, as you have doubtless noticed, are moving upward again. In a worldwide oil market, any disruption is going to be felt worldwide.

As for the public panic that Mr. Carter is trying to avoid, there's no better time than the present for letting people get used to the idea that things are going to get tight. If people are going to react by trying to fill up every tank and teakettle -- as they are already beginning to do -- it is best that they do it while there is still a great deal of oil around. By next fall, if things continue to go badly in the Persian Gulf, there may be much less slack in the system.

People talk as though $1-plus a gallon for gasoline were the end of the world. But among all the principal oil products, as a matter of enlightened social policy, gasoline surely deserves the lowest priority. First come heat and light -- that is, home heating oil and the heavy residual fuel that is burned by power plants. Next come fuel for aircraft and the feedstocks for the chemical industry. If there is to be a severe shortage, it will be less frightening to the public, and less disruptive to the economy, if the impact falls mainly on gasoline consumption.

Perhaps you feel that a tax nearly doubling the price of gasoline would be too costly, and too annoying. What would you prefer? The Iranian revolution has, in fact, reduced the world's oil supply. Iran is unlikely to export much oil for months to come. One effect is to increase greatly the dependence of this country, and every other industrial country, on Saudi Arabia. If anything were to happen now to Saudi production -- and it has been declining in recent weeks -- this country and its allies would be thrown into an economic convulsion on a scale that they have not experienced since World War II.

Americans continue to behave as though nothing were happening. Mr. Carter speaks of observing speed linits and lowering thermostats. If this country cannot substantially and rapidly reduce oil imports on its own terms, by its own action, it delivers its fortunes into the hands of other governments, present and future, in the Persian Gulf.