Santa Claus' data base just swelled by several megabytes, computer experts said Wednesday, after unknown letter writers bombarded his North Pole Internet address with thousands of Christmas letters.

"Santa got spammed," said Carl Malamud of Washington, referring to the practice, reviled in cyberspace, of sending out a bulk mailing of unsolicited letters or messages.Malamud, president of the Internet Multicasting Service, manages Santa's electronic mail, cookie recipe, Christmas jingle and volunteer information center on the global network of computers.

What started as a high-tech "Cyberspace Christmas" fund-raising effort by several civic-minded organizations appears to have backfired, at least temporarily, said George Paolini, corporate information manager for Sun Microsystems Inc. of Mountain View, Calif.

Sun was one of four companies that promised to donate 10 cents each time someone used the Internet's World Wide Web electronic publishing resource to read about a specific charity.

Although more than 30 million computer users worldwide are thought to have the ability to send electronic mail messages to Santa by using the Internet, only about 2 million people are believed to have the advanced technical tools needed to visit Santa's "home page" on the World Wide Web. People with access to the World Wide Web can visit Santa's Cyberspace Christmas center at the URL:

But at least some Internet users apparently misinterpreted the offer, thinking that Sun and the other companies, including Ex Machina Inc. of New York, would donate 10 cents each time Santa received an electronic mail letter.

Because there are no stamps in cyberspace, there is no penalty for sending lots and lots of letters. People started adding Santa's E-mail address - santa anorth.pole.- org - to the "cc" of every message they sent.

Quickly, word of the charity offer spread throughout the Internet, and programmers began sending "mail bombs" of hundreds of messages an hour to Santa to accelerate the donations.