SPLENDID. PRESIDENT CARTER'S energy program is, evidently, going to include a stiff tax on gasoline. That's a pretty good test of presidential purpose. An energy program that reaches gasoline consumption is a serious one, deserving respect and cooperation. Conversely, programs that step delicately around gasoline pricing are mere window dressing. But while the bite in the Carter plan is going to be real, it will also be delayed - the price, it seems, of getting it through a reluctant Congress.

The atual imposition of the tax is postponed, as we understand it, until 1979. There's to be an elaborate trigger mechanism. If next year's gasoline sales exceed this year's (as they certainly will) the tax would then come into effect. That puts the painful impact off until after the next congressional elections. To put the best face on it, you could argue that this long wait constitutes fair warning. But if you agree that American overconsumption of fuel requires forceful national action, you will probably also agree that two years is too long to wait for it.

Our understanding of Mr. Carter's program depends entirely, at this point, on the usual leaks, dribbles and hints that precede any great presidential initiative. The message will be formally presented next Wednesday - the promised three months, to the day, after he took office. Why do we not wait until then before commenting? Because this message will be central to American policy and politics for the rest of the year, and perhaps a lot longer. We'd rather err on the side of speaking too soon than too late. If the details of the plan are still abscure, the general thrust is fairly clear.

Mr. Carter and his energy planners, headed by Dr. James Schlesinger, have come down squarely on the right side of the crucial enforcement issue. They have chosen to restrain overconsumption mainly by raising prices and taxes, rather than by legal restriction and regulation. Regulation means, one way or another, rationing and, for 216 milliom consumers, it won't work. If there's one thing that this country doesn't need, it's squads of federal energy cops creeping off in pursuit of the energy addicts among us - those sinners who perversely overrun their allotments and quotas.

The right solution is heavy taxation to make those sinners pay. The revenue then has to be returned promptly to the public - preferably by cutting regressive taxes now in effect, like the Social Security payroll tax. It's a device to redistribute income away from people who use a lot of fuel to people who use less of it. But the flows of money here would be extremely large, and a great many members of Congress will also see in it other kinds of redistribution - from one income group to another, from one industry to another and from one geographical region to another.

In Congress, this immense programm is going to be treated much like a tax reform bill. Struggling to make it fairer by various conflicting definitions, the congressional committees will inevitably make it more intricate and less comprehensible. The legislation, after all, will include not only gasoline but the taxing and pricing of crude oil and gas. It will reach home insulation and the licensing of nuclear reactors. As with a tax bill, passage will be a divisive process and the narrowest interests will be the best represented.

This legislation will have no natural constituency. The old-line consumers' organizations will probably fight it because it raises prices. The automobile companies and unions fear that it will cost jobs and profits. The oil companies already see themselves penalized by a vast new taxation. People who commute by car aren't going to like it, and there are lot of them.

It's up to President Carter to explain why it's necessary to undergo all of this cost, trouble and disruption of our accustomed national ways. The explanation is readily understandable, although it's not a comfortable one. There's a real danger to the United States in its recklessly expanding fuel consumption when its own oil and gas reserves are declining. There's a severe and growing danger in this country's increased dependence on Middle Eastern oil - danger to jobs, to personal prosperity and to national security. This rich and fortunate country clings to its traditional sense of boundless abundance and, as long as gas tanks are full, its ideas are not going to be readily changed. Getting this legislation enacted is going to be difficult, at best. But if Mr. Carter speaks candidly of the great national interests here, and the rising threat to them, there's a chance that the bills will go through.