THE GASOLINE rationing plan is now legally in place. Is that reassuring? Does it mean the country is ready to deal with even the direst shortage of oil?

It will take another year and $100 million to get the regulations written and the coupons printed. But the main outlines of the system are established. Rationing would go into effect only in the event of a severe drop in oil supplies -- a shortage at least twice as severe as the one that caused the gasoline lines last year. A ration book would go to each car, so the three-car-family would get three times as much gas as the one-car family. It would be legal to buy and sell the coupons.

A few questions haven't quite been settled yet. How much will businesses have to cut back, compared with private motorists? What about the people who buy old cars to get the rations books? The Department of Energy is considering a limit on the number of ration books per household -- but it isn't easy to define a household, as the White House Conference on Families discovered. And then what about diesel fuel, which is the same thing as home heating oil?

The ration coupons would have a substantial cash value. In shortage sufficient to trigger the rationing law, a gallon of gasoline would be worth about $3, DOE calculates. If the price at the pump was $1.25, the coupon would be worth $1.75. Since people wouldn't want to walk around carrying hundreds of dollars' worth of coupons, the banks would provide coupon checking accounts. That's another checkbook to be balanced at the end of the month. But just a minute. Don't these coupons begin to look like money -- and act like money?

Of course they do. This whole intricate, expensive, parallel system of currency is being created for the usual inadequate reason. Congress thinks its constituents consider rationing fairer than a tax. Most of Congress understands that rationing is, in its impact, exactly the same as a tax with a rebate. But gasoline taxes are unpopular, and Congress likes to be loved.

At least the rationing system wouldn't be in effect long -- less than a year, if last year's experience is a guide. Rationing would tell foreign oil producers that their prices for crude oil were too low. They would raise their prices until supply balanced demand, just as they did last summer. A tax with a rebate would recirculate the higher costs of gasoline back into the U.S. economy. But when the foreign producers increase their prices, there's no rebate. Once again the president and Congress, in pursuit of a spurious idea of social equity, have constructed a mechanism that, in a crisis, would benefit primarily the foreign oil producers.