THE DEPARTMENT of Energy has submitted for congressional approval an emergency gasoline rationing plan it calls "the best we could devise." Although there will inevitably be criticism of this or that provision, the plan probably s the best possible rationing scheme. But a look at what it would mean in practice quickly reveals that this is one case in which there is an answer to the perennial question, Why not the best? It is that, where gasoline rationing is concerned, the best is just as unworkable as the worst.

Rationing under this scheme would be triggered by a presidential finding that the country was facing a 20 percent oil shortgage -- unless the Congress said no. (The exact size of the shortgage that triggered last year's gas lines is still unknown, but it was closer to 5 percent than 20 percent.) Once triggered, even after 12 months of "pre-implementation," costing $100 million, the system would require an additional three months of preparation -- a long time for gas lines -- before it could begin.

After the plan had been triggered, DOE would first have to determine how much gasoline would be available -- a crucial but uncertain calculation. After having made this determination, and having set aside a national reserve and amounts for farms, businesses plus other priority users, DOE would allocate the rest to states on the basis of past use. This is the same technique used in 1979 that resulted in flooding rural and resort areas with gasoline while urban areas endured three-hour lines. The reason was that during the shortgage, people (naturally) did not go on vacation in nearly the numbers they had the year before. Similar unanticipated shifts could be expected under the new system. After each state had set aside its own reserves and priorities, the remaining gasoline would be divided among ordinary folk on the basis of registered vehicles.

Since the coupons could be bought and sold, they would be as valuable as money, and therefore could not be sent through the mail. Instead, coupon checks would be sent -- to be redeemed for coupons at banks or other secure places. Even after several tens of thousands of new tellers had been hired and trained, however, lines at gas stations would likely be replaced by lines at banks. The value of the coupons put into circulation each year would amount to a second currency. All the accompanying paraphernalia of a currency -- vaults, armored trucks, protections against counterfeiting are among them -- would somehow have to be brought into play.

There are 150 million eligible registered vehicles: three times as many as the number of recipients of Social Security and food stamps combined. Since one-third of the fleet changes hands each year, it would be even more difficult to make coupon checks connect with their rightful owners. If only 10 percent went to the wrong address, 15 million vehicles would be without gas. Even worse, as soon as the program had been announced, many of those who could afford to would probably buy "junkers" in order to increase their allotment. At least that is the expectation. This type of fraud can only be partially limited by placing a limit on the number of allowed vehicles per household.

Aside from the businesses the state or federal government had pronounced priority-users, there would be millions of individuals who believed themselves to deserve a supplemental allocation. Panels similar to local draft boards would have to be created for the entire population. Administration of the system would cost a minimum of $2 billion a year.

Contemplation of this proposition should end the pretense that a standby rationing plan "prepares" the country for an oil emergency. It prepares it for nothing more than an expensive, divisive, uneconomic conflict. An alternative is available. Under it, the price of gas would be the same as under rationing, but there would be no coupon lines, no allocation boards, no huge new bureaucracies, no hassle. It is called a rebated gasoline tax. Its principal drawback is that on Capitol Hill, four-letter words may be printable, but that three-letter word, tax, is not.