Several weeks ago, there appeared in this space a warning that the Bell System had grown weary of being defrauded.

I reported that the telephone company's security department had developed new equipment and sophisticated procedures designed to detect fraudulently placed long-distance calls. I added that the front office had made a policy decision to catch the cheaters and prosecute them. No more Mr. Nice Guy.

It now appears that hundreds of students at American University either did not read the warning or, having read it, did not think the telephone company was smart enough to catch them. Alas, they were dreadfully wrong. On a recent evening, Bell System security equipment silently recorded the placing of more than 40 long-distance calls illegally initiated from American University dormitories. Thereafter, police and telephone company security people conducted dozens of "interviews" with students at AU. c

Having been an undergraduate myself, I have a modicum of familiarity with the attitudes and thought processes of undergraduates. On the basis of that familiarity, I would like to offer a suggestion.

I suggest that among the goals that colleges and universities set for themselves should be an attempt to teach undergraduates that they are not as smart as they think they are.

"The man who knows, he doesn't know knows more than the man who doesn't know he doesn't know" -- and one of the functions of higher education is to give young people an awareness of how much they do not yet know.

Damon Runyon spent his life fraternizing with the "smart money" crowd at race tracks and on Broadway, yet one of the few messages he preached in his many stories was that it doesn't pay to be a wise guy. However canny you are, or think you are: beware! You're about to encounter somebody a lot smarter. You can depend on it.

Runyon's father had warned him that some day he would meet a stranger who would say, "I'll bet you I can let you shuffle this deck of cards and when you finish I can made the jack of spades rise from the deck at my command." Runyon's old man had counseled: "Don't bet with him, because if you do, that jack of spades is going to jump right out of the deck and spit in your ear."

The principle involved is well known to gambling men: Don't bet on the other fellow's game. Protecting the integrity of the Bell System is Ma Bell's game, and you shouldn't bet against her unless you're prepared to pay for all the hour-long toll calls you thought you were making free, and also for the legal counsel you'll need to defend you against fraud charges.

Incidentally, this might be a good time for me to pass along another friendly warning -- this one to people who make abusive, harassing or sexually oriented anonymous calls.

Be advised that much of the electronic equipment that helps detect fraudulently placed calls is also being used to catch annoying callers who think their technique for remaining anonymous is foolproof.

Bell System security people have been policing their network for years and have long been familiar with all the techniques employed by those who misuse the system. If you match wits with them, they'll catch you -- even if you're the canniest undergraduate in your class.

And, as I said at the end of my previous column about the Bell System's new electronic defenses: Don't say I didn't warn you. POSTSCRIPT

Science freaks may wonder how the telephone company catches those who misuse the system, and whether wiretapping plays a role.

I can tell you this much: Ma Bell's new ESS (electronic switching system) makes it possible to trace calls through the use of a Dataspeed 40 and other electronic gear. The equipment records where a call originated, where it went, and at what time.

There is no eavesdropping, no wiretapping.Just cold efficiency. THESE MODERN TIMES

Speaking of electronics: Bob Orben is worried that the modern mania for electronic toys is going to undermine the normal parent-child relationship.

After all, he asks, "How do you tell a kid who has just destroyed three galaxies, seven star ships and two solar systems to go wipe his nose?"