There was entirely too much Christmas cheer at International Business Machines Corp. last week.

On Friday, an unknown prankster inserted a holiday greeting into the mammoth company's in-house electronic mail system, an IBM spokesman said. The greeting was programmed so that if the recipient followed its seemingly innocent instructions, multiple copies of it were sent out, chain letter-style.

The snowball effect overwhelmed the system's circuits and slowed down delivery of other mail.

The message popped onto desktop screens in IBM offices around the country and even crossed the Atlantic and Pacific oceans, showing up in IBM outposts in West Germany, Italy and Japan.

Late Friday, employes were put on alert to stamp out the overdose of Christmas spirit. Technicians shut down overloaded mail computers, went into them and extracted the offending material.

The message that bedeviled IBM was a comparatively benevolent one and did not, as computer tricksters' creations sometimes do, destroy other material in the system. It consisted of a picture of a Christmas trees devised from rows of the letter X and a holiday message:

"A very happy Christmas and my best wishes for the next year.

"Let this run and enjoy yourself.

"Browsing this file is no fun at all. Just type Christmas."

People who did so unwittingly became part of the prankster's design. By typing "Christmas," they triggered a program that caused copies to be produced and sent out in their names to other people on the automatic distribution system. Some of these people in turn duplicated it and sent it on, rapidly producing electronic gridlock.

The culprit is unknown, said company spokesman Andy Russell, but preliminary investigation suggests that the message originated outside the company. IBM's mail system is attached to those of several other institutions.

From start to finish, the message survived only hours, Russell said.

"The moral of the story is that security procedures are not a joke," said Charlotte LeGates, communications director for the Computer and Business Equipment Manufacturers Association. Unauthorized entry to computers has emerged as the signature crime of the information age.

LeGates said many companies and employes fail to realize the trouble they can face if they don't control access to the machines. "We still have people who will write their passwords on a note and stick it on a terminal," she said.

Does the world's biggest and most advanced computer company feel embarrassed about its Christmas chain?

"We didn't want it to happen," said Russell. "But we anticipated something like this might be attempted and we were prepared to deal with it."