Your Money : Don’t Let Crooks Shop on Your Credit : Consumers: Shoppers should be extra careful, card companies say, as fraud tends to skyrocket during the holiday season.

Armed with credit cards and gift lists, holiday shoppers crowded into stores and malls over the weekend.

So did crooks. Credit card crime tends to skyrocket in November and December, when people use plastic more than at any other time of year.

In recent weeks, card companies have sent customers warnings to be extra careful.

“The potential for fraud really increases during the holidays,” said Nancy Elder at New York-based MasterCard.

More fraudulent charges were made during the 1993 Christmas season than at any other time during the last 12 months, according to RAM Research Corp., a Maryland company that tracks credit card trends.

Fraud losses involving MasterCard and Visa accounts rose to $92.5 million in January from $85.6 million last November, according to RAM.

Since the beginning of this year, however, new technologies such as security-coded cards and computer systems alert to unusual account activity have been introduced. Fraud losses have declined so far in 1994 after rising for several years, said Robert McKinley, RAM president.

But he predicted that fraud will surge again during the holiday season. With more cards in circulation and consumers expected to use plastic more this year than last, the crooks could rack up $300 million in charges by Christmas, McKinley estimated.

That would be less than 1% of the $500 billion in charges that will be made over the whole year, but such losses mean higher prices because retailers must pay higher fees to the card companies.

Typically, the cardholder is not responsible for more than $50 of charges made on a lost or stolen card.

“Even if you don’t have to pay for all the charges, it doesn’t mean you won’t have a hassle straightening out the problems and getting a new card,” said Ruth Susswein of BankCard Holders of America, an association of 40,000 members.

The use of lost or stolen cards by thieves accounts for 70% of all fraudulent charges, so Visa encourages its customers to carry only the cards they intend to use on a shopping trip, said Albert Coscia, Visa spokesman.

Keep a list of account numbers and the card issuers’ 800 phone numbers at home in case you need to report loss or theft of a card, said MasterCard’s Elder.

If you never received a card you requested, call the issuer immediately. A lot of cards are swiped from the mail.

Most retailers have switched to carbonless sales slips, but some stores still use carbon paper. Elder said consumers should keep the carbons or make sure the clerk rips them up. Thieves can use account numbers on the carbons to charge telephone calls or create phony credit cards.

If you write a check for a purchase, don’t write your credit card number on it, Elder advised. Contrary to what some merchants may tell you, they can’t require you to give the number as identification or to “validate” a check. And they can’t use the account number to guarantee payment in case the check bounces, Elder said.

Make sure sales clerks give you back your card, not someone else’s. And put the card back in your wallet or purse immediately after the sale, said Elder. A card in a pocket is an invitation to pickpockets.