"Any excuse will serve a tyrant," wisely wrote the fabled Aesop. Today that remains the case. But most non-tyrants still feel required, when making excuses, to make them creatively credible. And for very good reason, because a well-constructed excuse can, among other nice things, prevent ugly confrontations and spare hurt feelings.

That's undoubtedly what Sally Sweetwater was doing, earlier this century, when she turned down my August invitation to the Thanksgiving dance by revealing that she would be washing her hair that very night.

And rather than candidly telling a teacher that his presentation is dull and uninspiring, the unprepared student can charitably explain: "The dog ate my homework." Both of these are, of course, veteran excuses with a number of miles on them.

An effective new excuse is about as rare as a silly bond salesman. But there is, at this very moment, just such a new excuse in limited circulation. The new excuse is not available to the general public, which is wrong: all excuses should be public property and none should be the private preserve of the powerful and the privileged. That is unfortunately the case with the hit new excuse: "the computer is down."

Take the case of the conscientious working stiff who worries that he might have overdrawn his checking account by failing to record a check. He calls the bank to determine if his account has any balance. On the other end, some bloodless wretch compounds our friend's misery by announcing: "The computer is down." Our anxious customer, with every logical right to be angry, is instead probably intimidated. In our culture, the computer speeds with the authority of Scripture (or at least of Paul Harvey) and is not to be questioned even when taking one of its frequent naps. Forget that old Mrs. O'Brien would cheerfully tell you your balance within a nickel, or that Mrs. O'Brien was almost never "down."

Many of us know little about computers or their special tongue. There are still a few people for whom a "program" is something on sale outside the stadium that lists the uniform numbers and home towns of the players.

Banks are not the only villians. Airlines and a lot of businesses with "800" telephone numbers employ the down-computer dodge. You can almost hear them humming what should be their theme song: "My systems are down. I've got you where I want you."

The politics of the problem begin to emerge. Who have the computers and, therefore, the exclusive franchise on this new and powerful excuse? Those who have the computers, of course, and who are mostly large institutions or very rich individuals. And who are those on the receiving end, the ones being intimidated? Those who have neither a computer nor computer access and who are therefore without access to that wonderful excuse as to why the oil bill is unpaid.

Debtors need excuses like the Russians need grain in ports. A lot. Most debtors are, by disposition, Democrats. This may be the opening the Democrats have been looking and praying for. If the Democrats, faithful to their ancient heritage, believe that "the-computer-is-down" excuse should be available to all--that it should be, yes, an entitlement-- then they could be on the verge of a major comeback in 1982.

By early next year, with limited federal loans, every American home could be sporting its very own lemon home computer, which would be guaranteed to be "down" most of the time. The excuse would be truly democratic, no longer limited to the big banks and corporations. All of us, when pestered by the phone company or--even better --the bank, could simply and haughtily respond: "You'll have to call back. My computer is down."