A group of retailers, led by Wal-Mart Stores Inc., is seeking $8.1 billion in damages from Visa and MasterCard in an antitrust suit that accuses the big bank-card associations of using their market dominance to force stores to accept their high-cost debit cards.

The case, which has been pending since 1996, received new impetus recently when a federal judge in Brooklyn refused requests from Visa and MasterCard for further postponement and scheduled a hearing next month on whether to treat the case as a class action.

The judge also granted a Justice Department request for access to evidence and other records obtained by the retailers for possible use in a government antitrust suit that is pending in another federal court in New York.

The private case, which includes many of the nation's largest retailers, involves the "interchange fee" banks charge when stores accept a debit transaction. When a customer uses an ATM card, the transaction is activated by a personal identification number and processed electronically, and typically costs about 8 cents.

However, if the customer uses a Visa Check Card or MasterCard's equivalent--which is often the same piece of plastic as the ATM card--the transaction is verified by the customer's signature and processed off-line. In that case the fee is 1.6 percent of the amount--64 cents for the typical debit transaction amount of $40, or $1.60 for a $100 transaction.

The retailers would like to refuse the Visa and MasterCard debit cards, but both associations have what they call an "honor-any-card" rule requiring retailers to accept any proffered valid Visa or MasterCard. Under this rule, if a retailer refuses a valid debit card, it could lose the right to accept Visa and MasterCard credit cards.

"It's a tying case," said Lloyd Constantine, of Constantine & Partners, the retailers' lead attorney. "Visa and MasterCard both say, 'If you take our credit cards, you have to take our debit cards and you can't refuse to take them.'

"The issue in a tying case is whether or not [the company involved] has market dominance," he added, and "with a retailer the size of Wal-Mart, if they are forced to take them, then where does a small retailer fall?"

Constantine said retailers treat the higher costs as part of their overhead; those costs are paid by all customers, not just Visa and MasterCard debit-card users.

Both Visa and MasterCard said the honor-all-cards rule ensures that consumers have the choices they want, and they expressed confidence that they will prevail if the case goes to trial.

Kelly Presta, a senior vice president at Visa, said Visa's rules don't prevent a merchant from "prompting" a consumer to use a PIN so that the transaction gets the lower fee. "You can incent for other payments, you just can't refuse the card" if the customer wants to use it, he said.

"Visa will vigorously defend the honor-all-cards rule because it is the cornerstone of what Visa stands for and is essential to the enormous benefits Visa and its members deliver to merchants and consumers," Presta said.

Constantine said that if the case is certified as a class action, it will probably include as many as 3.5 million to 4 million retailers "with 6,000 banks on the other side."

"Basically it's the retail industry against the banking industry, and that's good because it'll settle things once and for all," he said.

If the retailers prevail, the $8.1 billion value they put on their actual damages, a figure first reported yesterday by the Wall Street Journal, would be tripled to $24.3 billion under antitrust law.

Presta called the $8.1 billion figure "wildly irresponsible and inaccurate," and "based on a number of assumptions that all assume the worst case for Visa."

The Justice Department's case, filed in 1998, accuses big banks, which often belong to both Visa and MasterCard and issue cards under both names, of controlling both associations and acting to restrain innovation and stifle competition.