TO DEAL WITH the Japanese automobiles as he wishes to, President Reagan needs to invest a new three-lettered mechanism. The standard took kit of protectionalism offers the OMA -- which stands for Orderly Marketing Agreement, and is not always so orderly. It also provides the VRA -- the Voluntary Restraint Agreement, which is rarely voluntary. Both are quotas, designed to protect domestic industry from the hazards of foreign competition. But both are too stark and conspicuous for Mr. Reagan's present purpose. What he needs is the SVQ.

That's the Selectively Visible Quota, which, like the Good Fairy, can be clearly seen under some circumstances but remains totally invisible in others. The quota needs to be fully visible in Detroit, where it will be greatly applauded, but invisible in federal court when the American distributors of Japanese cars bring suit under the antitrust laws. It needs to be visible in Tokyo, but not in Europe, where other governments are looking for excuses to put quotas on American goods. It can never be merely translucent; no one must ever be able to see through it. Here in Washington, it's got to be especially variable -- always sharply in sight when Mr. Reagan is talking about jobs for American auto workers, but never when he's talking about the inflation that eats up their wages.

It's the inflationary force of the SVQ that diminishes its appeal. The American auto companies say that they need protection from imports to give them time to adjust. Adjust to what? Eighteen months ago they were saying that they needed the time to get the next generation of small, high-mileage cars into production to match the Japanese. But that generation of cars is now in production. The only purpose of quotas now is simply to force up the prices of Japanese cars, enabling the American manufacturers to raise their own prices without losing more sales to the foreigners.

Perhaps, instead of treating it as just another price increase, the political engineers ought to call it the RIC -- the Re-Industrialization Contribution. When you buy a new car, the Selectively Visible Quota will automatically add the RIC to the price. Congress probably won't make it tax-deductible, but it can properly be considered a charitable contribution. All good Americans believe that you should support the charity of your choice, and in this case you will have a choice of General Motors, Ford or Chrysler. True, inflation will run faster. But the customers will have the satisfaction of knowing they are doing their bit to help stave off the American transition to the smaller, tighter, more efficient automobile industry that can meet and beat world competition.