JUST AS YOU suspected all along, those soaring prices at gasoline stations have meant big money not just for OPEC, but also for big oil companies and service station operators.An analysis of Department of Energy statistics, coupled with other findings, shows that the big oil companies are taking nearly 11 cents a gallon more than they were a year ago, while service station owners are making an average of 6 1/2 cents more. These increases in gross revenues (not profits), plus a 29-cents-a-gallon increase that is going to oil-producing countries and companies, amount to an average increase of 47 cents a gallon over the last year.

Before dressing down that neighborhood service station manager, however, it's important to note that these statistics are broad averages and that many rretailers have been hard-pressed by higher costs of doing business -- from the prices and rents they pay oil companies to the supplies they are able to aquire and sell. Still, there is cause to wonder who is making how much from retail price increases.

Under federal price controls, the oil companies may pass on to dealers and the public only their increased costs for raw materials and other capital and operating expenses. In turn, dealers may pass along only this cost plus a margin of up to 16.1 cents a gallon. But as one regional manager for Exxon claims, the average Exxon dealer in Maryland has doubled his income since 1978.

Further adding fuel to the concern is a surrvey of 100 stations were selling at prices above federral ceilings. Some of these overcharges were good-faith mistakes, surely, while other were not. The findings, from a survey made by the staff of Del. Luiz Simmons (R-Montgomery), are disputed by area dealers, who say that overcharges occur only when station managers do not keep up with fluctuations in the wholesale prices. Mr. Simmons argues that, in the absence of an effective federal enforcement effort, overcharges could be corrected with a more agressive auditing program by the state.

To some degree, perhaps. But even without trying to calculate how much a dealer should make from sales, better auditing and public disclosure would at least let the public know more than it does today about where the money is going. Certainly service stations should display their prices on signs visible from the road, instead of those fine-print-on-the-pump scribblings you can't read a hose-length away. Also, why shouldn't the dealers post breakdowns of how much of the pump scribblings you price is going to dealers, to Uncle Sam, to the state, and so on? They used to do this, just to let people know how much the taxes were. A little more public disclosure just might produce some livelier competition for customers -- if dealers are still serious about bringing in more business.