THE ASSOCIATED PRESS reports that Tupelo, Miss., has cited 48-year-old Oma Cain for violating an ordinance against frequent yard sales. The ordinance says a person can hold no more than one such sale every three months. Mrs. Cain was ticketed for holding one earlier this month, on grounds she also held one in July. Not so, she says, while acknowledging a strong propensity to sell. "I haven't held a garage sale since March."

We don't know what Mrs. Cain did or didn't do in July, and we're as much for law and order as the next folks, but on this one we're for the accused. A yard sale can occasionally be unsightly, we'll admit that, but it is one of the few unarguably wholesome institutions in America. The Tupelo town fathers should find another outlet for their admirable zeal.

Forget for a moment the obvious civil liberties and property-rights issues involved. Consider simply the good that yard sales do. They add their little bit to the velocity of M-1; they move the money supply around. They are antihoarding, and therefore good for character. They help create a more contented and more settled society, in which each object, as well as each buyer, finds its level. Are you a purple-glass-vase person (though perhaps a little ashamed of saying so in formal settings)? Are there not also some banished vases of just such purple hue on dusty shelves around your neighborhood? What can be more useful than a sorting device that shifts such objects painlessly from people who don't want them to people who do?

There are some aggressive types who think the country would be better off if everyone were made to buy new. Think of the jobs. But we've had too much of this over the years, too much throwing away. Conservation is the better ethic. The landfills of America would long since have brimmed over without yard sales; a great fleet of barges would even now be wandering over the oceans looking for places to deposit all those waffle irons, flowered lampshades and the rest.

Here at last is an issue where free enterprise is good for the environment, and for much else. Surely Tupelo doesn't want to spoil that. Let the people sell.