THE KEY FIGURE in the consideration of gasoline taxes is the involuntary driver -- the person who has no real choice but a car for getting to work or to the store. In the Republican presidential candidate's debate last weekend, Sen. Howard Baker cited that kind of driver as his reason for opposing higher taxes on gasoline. A great many Americans, Sen. Baker aruged, live in communities with little or no public transit.

Sen. Baker is exactly right, excepting only that he has it backward. When gasoline shortages appear, it is the involuntary driver who suffers most -- the person who, last spring, was out of bed before dawn to get in line at the filling station. But it is also this selfsame involuntary driver who now has the greatest stake in an effective fuel policy -- one that reduces the frequency of gasoline shortages, and limits their impact.

Sen. Baker is not alone in his error. All of the candidates -- with one interesting exception -- have said much the same thing. Because some people need gasoline badly for some of the things they do, this argument holds that it is unfair to tax the stuff for anybody. But does anyone seriously argue that this country is even approaching the limits of gasoline conservation? Weekend traffic is down a little on the roads to the parks and resorts, but not by a huge amount. More people are taking the bus, but the parking lots are still crowded at the big suburban shopping centers -- including those enjoying good bus service.

And that is where Rep. John B. Anderson (R-ILL.) comes in. He alone, among the candidates of either party, supports a gasoline tax of 50 cents a gallon. But anyone who "has to drive" ought to support that tax to cut down the frivolous and optional use of gasoline. Since Mr. Anderson would use the revenues to reduce Social Security payroll taxes, the average family would come out about even. The person who commutes long distances by car would pay more. But that commuter has to choose between spending more money for gasoline, or spending more time waiting in line when the next squeeze comes. If the federal government wants to intercede for the involuntary driver, Mr. Anderson's gasoline tax is in fact the simplest and most direct way to do it.