The woman had received an offer in the mail promising six months' free membership in a credit card protection plan that would keep a record of her card numbers and report any lost or stolen ones for her. All she had to do if she had a missing card was to notify the credit card protection company and it would do the rest: report the losses to all of the card issuers, cancel the old cards and arrange for new ones to be issued.

She signed up immediately for the plan offered by the Credit Card Service Bureau, an Alexandria-based company. She supplied CCSB with her card numbers and signed a statement that she understood the terms of the protection plan.

But she was shocked by CCBS' response, saying that her enrollment in the six-month plan entitled her to five years' extended membership and telling her that a bill for $35.40 had been submitted to her Visa account to cover the cost of that membership.

"I never said I wanted extended protection," the woman wrote in her complaint to the Alexandria Office of Consumer Affairs.

But, in fact, when investigators checked they found the woman had signed her name to this statement on the CCSB form: "I understand that my credit cards will be fully protected by the bureau, free for six months, and I also want to continue this protection for the 60 months thereafter at a special introductory member's fee of only 59 cents per month, billed upon receipt to either my Visa or MasterCard."

That works out to $35.40--the amount that the credit card protection company had charged to the woman's Visa account.

When questioned about the charge, CCBS dropped it and the woman ultimately wasn't obligated to pay anything.

But her complaint is typical of the complaints that consumer agencies are receiving because of a boom in the credit card protection business, which is making money off consumer fears of what might happen if their cards are lost or stolen.

In one mailing recently sent to Washington area residents, CCBS called attention to those possibilities with a flier that said, "Over 73,000,000 credit cards vanish each year . . . it's almost an epidemic, and if you wonder whether it might happen to you, the answer is clear, yes it can!"

According to the Nilson Report, a credit-card newsletter, about 6 million of the nation's 94 million card holders have registered with a protection service, compared to about 2.8 million in 1980.

Credit card protection is viewed as a legitimate business, but thousands of card holders have complained about the way that some of the companies operate.

The CCBS, for example, was cited by the Federal Trade Commission in the early 1970s for misrepresentations and was ordered to include a notice in its literature telling consumers that they wouldn't be liable for more than $50 if a card were lost or stolen.

CCBS attorney Michael Kushnick said refunds are made routinely to anyone who misunderstands the terms of the membership agreement. He said CCBS believes it has "very few complaints" when compared to the millions of pieces of mail sent out by the company.

But some consumer authorities question whether the average consumer really needs any credit card protection plan in view of the protection built into the federal law.

"The maximum amount for which a consumer can be held liable for unauthorized use of each lost or stolen credit card is $50," said David Grimes, an FTC attorney specializing in credit.

Moreover, he said, "If the consumer notifies the card issuer that the card is lost or stolen, then the consumer can't be held liable for any unauthorized use that occurs after that notification."

Sarah J. Hughes, another FTC credit specialist, said consumers can take some simple steps and protect themselves.

"The consumer who chooses not to buy the protection service could keep a list of his cards, card numbers and the phone numbers to call in event the cards are lost or stolen," Hughes said. "I would keep one list at home, one list at work and, if traveling, one list in a suitcase separate from my credit cards."