Explaining that they "do not like the nature of your business," Master Charge is trying to remove its credit card service from pornographic bookstores in the 14th Street area.

But four of the shops and one adult bath in the 14th Street area have joined with five Baltimore sex stores, one in Fayetteville, N.C., and a business service representing all the stores to sue Master Charge for $3 million. The suit also asks the U.S. District Court in Baltimore to enjoin the Maryland National Bank from removing Master Charge's machines from the stores.

"Their morally upright customers are bringing the cards in here," said the manager of one of the 14th Street area sex stores. "We don't ask them to come in here. Anyway the people who use the credit cards are businessmen and the suburbanites. Maybe Master Charge should go talk to them."

The suit against the Maryland National Bank and Interbank Card Association stems from a June notice the sex shops received from the bank notifying them that their Master Charge memberships were being cancelled and ordering the businesses to return their Master Charge credit machines to the Maryland National Master Charge Center in College Park.

The suit, filed Friday, contends that the bank and Interbank Card discriminated against the businesses and made "moral judgements," about the adult stores and their customers that "are not among the powers of a national bank," under the National Banking Act.

"This place is not any sleazy little bookstore," said an employe who answered the telephone at LeSalon, Inc., bookshop at 804-810 14th St. NW. "This place is plush. We have a standard joke here that this place is the Garfinckel's of porn, the Bloomingdale's of smut."

According to the suit, a salesman for the credit card company asked the stores to become members in the 110-nation chain of stores that accept Master Charge credit cards. The first store the salesman went to was the Capitol Book Store at 1401 H St. NW.

"These were extremely profitable relationships on both sides," said Barbara Gold, the attorney for the sex shops and their business agent, "so nobody had any complaints. The salesman came into the store in Washington seeking the account.He clearly knew from the instant he set foot in the store what type of store it was. So the bank didn't just suddenly find out, unless the word suddenly filtered up to the top."

The sex shops reported to the court, in papers filed with the suit, that the businesses profited a million dollars annually through credit card sales.

"Word-of-mouth grumbling of customers could convert the plaintiff's (the sex shops) inability to honor Master Charge into a reputation for general unreliability as a marchant," the attorney argued.

Gold represents the following stores: in Washington, Capitol Books, Inc; 13th Street News Inc.; D.C. News Center Inc.; LeSalon, Inc.; 1405 H.U.P. Inc; the Olympic Baths; in Baltimore, Fayette News Center, Inc.; Baltimore News Center Inc.; The Little Store, Inc.; Gallery News, Inc.; G & B, Inc.; and in Fayetteville, North Carolina, Bragg News, Inc.