SERVES them right. Even if Orlando J. Tardencillas, the administration's unreliable Nicaraguan captive-witness had said what it hoped and expected he would, his testimony would have been worthless for the purposes it had in mind. Certainly it would not have provided the "clincher" evidence his stage managers apparently thought it would. For war stories and personal narratives and individual young soliders' or bystanders' accounts, no matter what they allege, simply do not rise to the status of proof of anything. They do not begin to make the case the administration needs to make. On the contrary, even when the script is followed, they raise suspicions. They may serve as illustrations of a point already established, but in themselves they not only don't establish anything, but actually tend to invite skepticism. Mr. Tardencillas, in other words, was the equivalent of a living, breathing anecdote.

There. We said the terrible word: "anecdote." That is what Sen. Packwood accused Mr. Reagan of habitually offering up in response to (and in place of) serious argument concerning his economic program. And that is what others have also said the president repairs to when the discussion gets hot. There is some truth to all this; it bears on the Tardencillas affair, and it is important. But no one with a modicum of fairness could discuss it without acknowledging first that the technique is not a monopoly of Mr. Reagan's, never mind how immoderately he employs it. His predecessors have favored a stream of innocent-little-girl anecdotes--from LBJ's correspondent who wanted him to settle a railroad strike so she could visit her grandma or something to Mr. Nixon's Tania to President Carter's own little daughter whose concern about nuclear-weapons proliferation had such force, or at least so he thought. And whereas the right has its welfare queen stories, so the left has its poor folks living on dogfood counterparts.

What all these have in common (and here we get right to the lesson the administration should draw from its ghastly embarrassment by Mr. Tardencillas) is that these little heart-renders and point- provers not only invite the malign attention of the press (justly), but they also have damn near spawned a whole cottage industry dedicated to disproving them. Most of these anecdotes have a half- life of about 20 minutes--or until the first press run or the six o'clock news, whichever comes first. The only other real life, actual "anecdotal" people who come to mind, in addition to re-defector Tardencillas, are those carefully selected, middle- American folks the Carters liked to drop in on and who from time to time turned out to have some major flakiness or flaw the press would set about uncovering before the president had even had a chance to make his bed and steal away.

When Mr. Reagan points out that the convicted criminal known as Son of Sam gets Social Security payments, you may sigh or gasp. But you, as well as the hotshot reporters who get on the case at once to see if it's true, also know something else: that even if this is true, it neither establishes nor defines the problems of the Social Security system--which, whatever else they may be, are not that the system is going bankrupt because of payments to people serving terms for multiple murder. Mr. Tardencillas' tales-- tale I, tale II or (may there not be?) tale III--have about the same quality as proof. It was reckless and ridiculous for the administration to have trotted him out in place of serious exposition and argument.