RATIONING GASOLINE is getting to be quite a popular idea - because, people explain, it would be fairer. Congress defeated the administration's stand-by rationing plan last spring, but there is now much anxious talk of reviving it. After all, who wants to spend the summer waiting in gasoline lines? The only other way to avoid the lines is to impose a really stiff tax and - as most people agree, especially people in Congress - coupon rationing would certainly be fairer than that. Well, wouldn't it?

Before you join the crusade for social justice through rationing, you might want to consider the rationing system as it would actually work. Under the Carter administration's plan, and every other serious proposal since the Arab embargo five years ago, it would be legal to buy and sell ration coupons. The government would set the total amount of fuel to be consumed by passenger cars nationwide. Currently, it's just over one gallon a day for each person over the age of 16, if you need more than that, you can buy coupons from someone who can get along with less.

The price of the coupons would be left to the free market - with a vengeance. There would be no limits to the heights to which it could go. Since there's been occasional panic in the gasoline lines, might there not be panic in the coupon market? Try this little questionaire: Multiply the number of people in your family by 7 gallons a week, and ask whether you would be a buyer or a seller of coupons. If you are a buyer, how much would you be willing to pay for them?

Opponents of higher gasoline taxes cite the cases of poor or near-poor workers who have to drive long distances to their jobs. These people deserve careful consideration, for they would be the first victims of rationing. They need more than a gallon a day to get to work, and they would have to bid for it on the market. This system would be efficient and, like any free market, ruthless. It should be reserved for the most extreme emergency.

This kind of rationing would redistribute income massively - but blindly. Some of the beneficiaries would be poor people. Some would be much more prosperous people who have the good luck to live close to shops and Metro. Rationing would suck money out of poor regions like Appalachia, and pour it into metropolitan areas with good public transit. The appeal of a heavy gasoline tax is modest but, in comparison with rationing, a tax is clearly preferable. People would know exactly what was coming and, if Congress were wise, the revenues would be used to cut the Social Security tax for all working people equally.

The chance that Congress will enact a heavy gasoline tax is close to zero. But if the country embarks on rationing, it will have chosen a fiercely competitive biddign system that takes little account of social equity.