THE AMERICAN THIRST for oil is growing, as President Carter put it, "by leaps and bounds." The country is going to set another record for oil consumption this year. For a man who once called the energy crisis "the greatest challenge our country will face during our lifetime," Mr. Carter seems to be watching the oil figures with remarkable equanimity. At his press conference on Thursday, he was asked whether he isn't going to have to take far more rigourous action to enforce conservation. But the answer was no, he doesn't have anything further in mind for the present.

In an interview on Friday, Mr. Carter went two or three inches farther and suggested that further government action - unspecified - may be necessary. He seemed disappointed that oil consumption is following all the standard forecasts upward. But it ought to be pretty clear now that intermittent presidential appeals for voluntary cooperation, interspersed with long silences, are not going to carry conservation very far.

The dilemma here is evident - and it's not just Mr. Carter's dilemma, but he whole country's. Any sudden and drastic restrictions by the government to cut down oil imports would shake the economy and increase unemployment. It there's one thing on which the President and Congress are fully agreed, it is the imperative that conservation policy must not threaten economic growth or the standard of living. That's why the Carter energy plan, as it originally arrived last April, would have taken effect only very gradually. That's also why the plan, as Congress is now amending it, will take effect even more gradually and gently. Under the Carter plan, by every estimate but Mr. Carter's, the country will be importing somewhat more oil in 1985 than it does today.

There's an unspoken assumption in the plan that the oil-exporting nations will continue to produce and sell as much as its customers want to buy. As assumptions go, that's not a terribly safe one. There's a large and obvious probability of stiff increases in the price of that oil, not only in money but also in terms of political concessions and privileges. The President understands that point perfectly.

It's difficult to grasp the strategy that he's been following in the long silence those electrifying speeches last April. "We must not be selfish or timid if we hope to have a decent world for our children and grandchildren. We simply must balance our demand for energy with our rapidly shrinking resources. By acting now we can control our future instead of letting the future control us." Remember that? He said it three months ago. Since then, he and the people around him have changed tone entirely. The wholw discussion has become cool and detached. Conceivably, Mr. Carter calculates that Congress will work more efficiently - and faster - if he does not get people excited. Conceivably, he believes that even the forthcoming legislation strains the limits of political effect before the early 1980s.

It's also very possible that he is apprehensive about reminding the oil-exporting countries of American vulnerability. If that's the case, the dilemma is compounded. It would mean that Mr. Carter felt himself unable to continue talking candidly to the country about decisions that, he said in April, will test "the ability of the President and Congress to govern this nation."

But there is one fortunate thing about the struggle over energy. It is essentially fairly simple, and citizens can follow it through a few basic numbers. In the four weeks ending in mid-July, according to the government, this country used 4.7 per cent more oil than it did at the same time last year, and it imported 12 per cent more. If you know that, you know what's going wrong.

Mr. Carter's energy policy take it for granted that the world will allow the United States 10 years' grace to get its thirst for oil under control. But Americans need to begin thinking urgently about the unpleasant possibility that the future may not be nearly so generous.