In their overreaction to a new Maryland law that bans them from charging dealers a processing fee for gasoline credit card purchases, some oil companies may be overlooking an opportunity to increase their income in the state.

At the same time, by barring oil companies from charging dealers the 3 percent processing fee, Maryland's General Assembly may have helped the banking industry in an ironic twist of events.

And while the law is subject to various interpretations by major oil companies, consumers and dealers are caught in a web of confusion.

For one thing, banks can charge dealers a processing fee for accepting bank credit cards, while oil companies may not assess a fee.

The same law that bans the 3 percent processing fee that the oil companies sought raises the maximum interest rate on all credit card purchases from 18 to 24 percent.

But instead of devising a way to pass on the processing fee to consumers within the 24 percent interest rate limit, several of the oil companies have decided to pick up their marbles and go home because they couldn't win the fee issue.

Texaco, for example, announced it will drop credit cards in Maryland after July 1, when the law goes into effect.

Mobil, on the other hand, has added to the confusion of consumers and dealers in letters to both.

Effective July 1, Mobil cardholders won't be allowed to buy diesel or aviation fuel with their cards but may continue using them for other gasoline purchases.

However, Mobil will not accept credit card applications from Maryland residents after July 1. Moreover, Maryland residents will not be eligible to use their cards for gasoline purchases in cities outside the state where Mobil is conducting a discount-for-cash/service charge program.

A Mobil spokesman denied that the company is taking punitive measures against Maryland residents because of the new law.

He said that the law is a "highly complex issue subject to varying interpretations." As a result, Mobil has decided to put a hold on issuing new credit cards "until things are sorted out," he said.

Meanwhile, any attempt to charge cardholders the maximum 24 percent interest in lieu of the disallowed processing fee "is not without risk," the spokesman added.

But "there's nothing in the law that prevents the oil companies from increasing the finance charge up to 24 percent," says Carl Eastwick, chief legislative aide to Maryland Gov. Harry Hughes.

"I think that what can be derived from this legislation is that all extenders of credit will have to roll in their finance charges" under the 24 percent ceiling, Eastwick said.

In an attempt to clarify the various interpretations of the law, Mobil has written to the Maryland General Assembly asking further explanations.

Like some oil companies, Maryland's banking industry balked at being prohibited from charging an annual fee for bank credit cards. In fact, several Maryland banks decided to move their credit card operations to Delaware, where they can charge fees and unlimited interest rates.

And while the oil companies are banned from collecting processing fees on gasoline purchases, issuers of bank cards are allowed to collect fees from dealers ranging from 2.35 percent to 2.95 percent.

"Why should banks be allowed to charge 3 percent if the oil companies can't?" asked Marcellus Bowie, operator of a Texaco station in the 9600 block of Livingston Road in Prince George's County. "I think there should be some investigation of that."

Nonetheless, Bowie plans to accept bank cards for gasoline purchases after July 1.

"Without credit cards, the small businessman will be hurting," predicts Ron Muncastle, owner of a Mobil station in Oxon Hill. "It's like teaching a baby to eat candy and taking it back from him," Muncastle said of the aggressive marketing of cards by oil companies before their decision to restrict their use in Maryland.

Despite severe restrictions that some oil companies are placing on Maryland holders of their credit cards, Muncastle is certain dealers will suffer more. "If people don't have an oil credit card, they're likely to have a bank card," he pointed out.

Fearing a substantial loss of business with credit card restrictions, several dealers, like Bowie, are preparing to accept bank credit cards from their customers.

But while dealers may choose to accept bank cards, they have no choice in their dealings with the oil companies, maintains William Shoemaker, executive vice president of the Greater Washington Maryland Service Station Association.

The association lobbied succesfully for passage of the bill that bans the processing fees, contending that oil companies were in a sense double-dipping by tacking on the extra charge.

Now, Shoemaker thinks he has another solution to the credit card debate. "I think some enterprising company will come up with a universal credit card for gasoline," he predicted.