THE LATEST DEFEAT in the Senate for President Carter's energy plan is genuinely alarming. The senators have knocked out one section after another in the month that they have been working on these bills. But the key to the plan was the series of taxes on crude oil and industrial fuels. Until a few days ago it still seemed likely that the Senate Finance Committee would perform its usual ritual: first the prolonged war dance in which it mutilates the tax bill with infinite loopholes and preferences, then the conference with the House in which most of the worst excesses are compromised out.But now it appears that the truth is simpler. Most of the senators don't like the President's strategy of using taxation to enforce conservation, and they won't support it.

The chairman of the Finance Committee, the redoubtable Sen. Russell Long (D-La.), has evidently lost control of it altogether. He has fallen back on a scheme to report a skeleton bill containing nothing but tax breaks. He would leave the actual job of writing the tax legislation to the Senate-House conference. That prospect is enough to terrify anybody familiar with the confused and turbulent atmosphere of a conference on a major bill. Of course, the Long scheme may never develop. It would require the House to carry the responsibility for having levied the tax, while the senators reap the political benefits of having introduced the exceptions and dilutions. It is not a division of labor that greatly appeals to the House.

The revolt in the Finance Committee culminates a bad month in the Senate. It has accepted none of the main elements of the Carter energy plan, flatly rejecting some of them and gravely weakening the rest. It greatly widened the exceptions in the bill to convert industry to coal. Regarding automobiles, it did nothing but ban those cars so grossly inefficient that, under present law, very few would ever have been produced anyway. It voted to deregulate natural-gas prices, which Mr. Carter wants to keep under controls.A few days ago it finally passed the electric-utility rate-reform bill in emasculated form, giving the new Energy Department the authority to do nothing more than to argue in state regulatory proceedings. Now the whole effort to pass the oil and industrial fuel taxes has collapsed, and this is a more serious defeat than all the others put together.

If the senators don't like the Carter energy plan, what do they suggest? They all know perfectly well that the United States cannot afford, financially or politically, to keep increasing its oil imports. They all understand that the present oil price system actually subsidizes imports - an anomaly that Energy Secretary James Schlesinger accurately termed "ludicrous" the other day. The senators realize as well as anyone that the present degree of this country's dependence on foreign oil is dangerous. What do they prescribe other than taking two aspirin and hoping for the best? Their version of the energy plan so far consists mainly of giving you a tax credit for insulating your attic.

The Energy Department puts out a weekly oil bulletin, and the latest one notes that American demand for oil is currently rising at a record rate for this time of year. Demand for oil is now running a fat 6 per cent higher than a year ago. Imports are 10 per cent higher than a year ago - and imports, incidentally, now make up 48 per cent of all oil consumed in this country.

The central structure of Mr. Carter's energy plan may already be beyond rescue. But if there is a chance to save it, that chance lies in immediate and vigorous intervention by Mr. Carter himself. He would be severely mistaken to assume that the House's bill, passed in early August, offers him a strong position from which to work in a House-Senate conference. Momentum accounts for a great deal in congressional politics, and since the August recess the momentum has been running strongly against the energy plan. The country and its Senate need to be reminded of the reasons that the energy plan is the most urgent legislation of the year and - as Mr. Carter said six months ago - essential. Since then, there's been a spreading impression that Mr. Carter's interest in the subject has diminished. If he wishes to correct that impression, he does not have much time in which to do it.