Riggs National Bank is exploring a number of alternatives relating to the future of its Central Charge Service Inc. subsidiary, including its possible sale or relocation of the division to Delaware.

Riggs officials have discussed a possible sale of the credit card subsidiary with at least a half dozen prospective buyers, Daniel J. Callahan III, the bank's president, confirmed. Callahan declined to identify these firms but added, "There are people who are interested."

Contrary to reports circulating in local banking circles, Callahan flatly denied that Suburban Bancorp in Maryland is among those with whom Riggs has discussed a possible sale of Central Charge.

Callahan observed that the credit card business has been tough in recent years. Moreover, he said, high interest rates and usury limits have "created a problem."

"We are exploring the various possibilities that might be available with Central Charge," he added.

One of those possibilities is a relocation of Central Charge to Delaware, where out-of-state banks increasingly are moving their consumer credit operations to take advantage of more liberal laws on interest rate ceilings, Callahan said.

Maryland's biggest banks either have moved, or plan to move, their credit card operations to Delaware.

Maryland National Corp., for example, maintains that its MasterCard operation has been unprofitable for some time. As a result, Maryland National, the region's largest banking institution, has formed a new subsidiary, Maryland Bank N.A., in Delaware.

Effective March 16, all of Maryland National Bank's MasterCard accounts will be assigned to the Delaware subsidiary. MasterCard customers who use their card for credit purchases after March 15 automatically agree to pay an annual fee of $18.

In addition, because Maryland National's credit card operations would be governed by Delaware laws, the annual percentage rate for MasterCard purchases will be 18.9 percent. Currently the rate in Maryland is 18 percent on balances up to $700 and 12 percent on balances above that.

Operating as a Delaware corporation, Central Charge conceivably could charge fees and annual percentage rates similar to those outlined by Maryland National.

Currently, District law permits an 18 percent finance charge on revolving credit balances under $500 and 12 percent on balances over $500. However, an amendment that is due to become effective shortly will increase the allowable rate to 18 percent across the board.

The Virginia Senate this week approved a measure that would eliminate the 18 percent ceiling in that state.

Central Charge was founded as an independent operation in 1952 and was purchased by Riggs in 1968. At one point it was the largest independent credit card operation along the Eastern Seaboard and the second- or third-largest in the United States.

More than half a million persons own the Central Charge card, which is accepted by more than 9,000 area merchants. Although inflation and high interest rates have affected the entire credit card industry adversely, "there hasn't been any appreciable erosion" in Central Charge's customer base, said Harry M. Schoenly, president of the Riggs subsidiary.

Schoenly acknowledged that Central Charge hasn't marketed the service aggressively since the credit crunch hit. But he explained "it wasn't economically feasible to go out and put more accounts on the books."

Callahan described Central Charge as a "tightly run business" and insisted that "our customer base has held up well."

However, persistently high interest rates have made consumer lending difficult, he said.