E-commerce is already a $24-billion-a-year consumer business in the United States. But imagine how much bigger it could be if two out of three consumers who browse shopping sites weren't afraid to give out their credit card numbers online.

The irony is that buying books, clothes or airline tickets on the Web now is as safe as handing over a credit card number to a waiter or making a catalog purchase over the phone, according to major credit card companies and banks.

And now that electronic commerce is a significant economic force, the federal government, merchants and consumer groups are forming coalitions to collect data on online fraud and educate consumers about the real risks when they use their credit card online.

Internet merchants also hope that positive word of mouth from consumers such as Van Nuys resident Tary Alpizar, who regularly shops on the Internet, will encourage more of the 27 million online households to take the e-commerce plunge.

Alpizar, who spent about $300 for household items on one site, relies on the Internet to help her buy videos and airline tickets and order documents such as birth certificates. "I've never had a problem," Alpizar said, "but I only use secure sites, and my computer tells me if I have approached an unsecure site."

About 95% of consumer online purchases in the U.S. are made with credit cards, according to Jupiter Communications, a market research firm in New York. Security experts agree that this method adequately protects consumers because banks that issue credit cards are required to reimburse cardholders for fraudulent online charges over $50, as they do for conventional retail purchases.

"Many online merchants are covering that $50, so the consumer's liability is essentially zero," said Ken Cassar, a digital commerce analyst at Jupiter.

The world's largest credit card network, Visa USA Inc., said the rate of online credit card fraud is similar to that associated with traditional credit card purchases. Last year, Visa had a fraud rate of 0.7%, amounting to about $427 million of Visa's $610 billion in retail transactions in the U.S.

An examination shows why it's difficult for a thief to steal a credit card number during an online transaction.

* Consumers should be sure they're using a secure Web site before making a transaction. A site is secure when a graphic that looks like a key or padlock in the lower corner of the browser is in the closed position and the letters "https" appear in the Web site address, instead of "http."