PEOPLE WHO ADVOCATE gasoline rationing, like Sen. Edward M. Kennedy, believe that it is both fairer and more effective than a tax to discourage driving. If the country wants to cut oil imports, the argument goes, it can simply set a limit to the gasoline supply, give drivers coupons for their shares and watch consumption drop. If a driver wants more coupons, he can buy them from someone who doesn't need the full allotment. President Carter is drafting a rationing plan, but would invoke it only in a dire emergency. Sen. Kennedy has now brought out his own plan, and declares that he would impose it immediately.

Currently, the average driver uses about 12 gallons of gasoline a week. Sen. Kennedy would use rationing to cut that amount, over a period of three years, to nine gallons. It would reduce oil imports by one-fifth their present level. So far, so good.

But how would the system actually work? That average rate of comsumption includes everyone from deliverymen and taxi drivers, on the street all day, to people who don't own cars and use their licenses only for cashing checks. Before you could divide up the nation's gasoline supply, you would have to set aside special supplies for high-priority services. During last spring's gasoline shortages, priority lists developed very rapidly. Farmers and fisherman are at the top, since nothing must interfere with food production. Then come the police and fire departments, the postal service, the utilities, the coal miners and the rest. Americans are very good at thinking up claims for priority, and Congress is sensitive in responding to them. Sen. Kennedy would give each state a further 5 percent set-aside for hardship cases to be adjudicated by local boards. He also thinks that in states where people have always driven a lot, drivers ought to get more gasoline -- a principle that may seem fairer in Texas than in Maryland.

When you add up all of the priorities and special allocations and set-asides, you are going to find that not much gasoline is left for the ordinary, run-of-the-mill, non-priority driver standing patiently at the filling station with his coupon. All commercial users, and many commuters, will have to buy coupons. Since not all businesses or all commuters will be able to afford them -- and no one can say how high the coupons' price would go -- the hardship cases will rapidly multiply. As the system makes more provision for these cases, the squeeze will get harder on everyone else and the coupon prices will spiral higher.

Rationing cannot avoid the hardships and inequities inflicted by the sudden reduction in oil imports that is now necessary. A tax is a blunt instrument, but it is simple and leaves everyone to adjust in his or her own way. Rationing subjects everyone to a constantly fluctuating coupon price, and a complex code of changing regulations that can create inequities as well as remedy them. Our guess is that the whole experiment would become unmanageable and, within a year or two, would collapse under its own weight.