They're a thrilling sight: feral horses, in herds big or small, galloping through the badlands, clear skies ahead and a haze of dust behind. For most westerners lucky enough to get such glimpses, they tend to be distant ones, adding to the mystique: the wild, the free ...

And, for a time, the few: Their numbers dwindled during most of the 20th century as more and more pastureland was closed off to them, and as they were hunted down for horsemeat and rendering, while the best were broken as saddle-horses. Their plight brought calls for protection, and Congress in 1971 passed the Wild Free-Roaming Horses and Burros Act. It commanded both the Agriculture and Interior departments "to achieve and maintain a thriving natural ecological balance" on our public lands.

That's a fine sentiment, if you don't think very hard about it — just pass a law and our Hollywood-fed consciences are clear on that photogenic and emotional issue.

But Audubon magazine commentator Ted Williams in recent years has given it lots of thought. Among his conclusions — most of them highly unpopular — is that the federal mission imposed by the wild-horse act is impossible: Horses, and burros, can't exist in natural ecological balance; in today's form, they're alien to the New World's ecology. And in their growing numbers, they're a threat to it.

The Spanish were the first to bring them here, he acknowledges, but notes that the myth of the feral herds being mustangs that got away from the conquistadores is just that; they're mongrels, notes Williams, a mess of some Spanish blood and more modern breeds — many of them discarded by folks tired of horse-ownership responsibility.

As for their movie images as muscular beasts, well, that's the advantage of seeing 'em from far away: Too many of those imaginary steeds are bony and mangy nags up close. But in numbers — fast-growing, according to some federal experts — those animals are capable of all kinds of environmental damage, even to the hardy sagebrush covering so much of the West.

On Bureau of Land Management property alone, there are more than 30,000 running loose. Another 25,000 or so are penned up for adopting, but with only a quarter of that number finding homes, the feds have a lot of horseflesh on their hands, and they have to care for it, instead of keeping campgrounds open, cleaning up illegal dumps and fixing roads.

New Mexico has maybe 600 feral horses wandering around, but most are in rugged stretches of Nevada and Wyoming. But even in those bleaklands, they're devastating to the natural inhabitants. They tromp down streambeds and destroy wildlife breeding-grounds. They're tougher on sage-chicken habitat than the oil and gas wells proliferating and proposed in many of the Mountain West's bleaker stretches, and they're a major threat to the lands of bighorn sheep, deer and pronghorns. They make grazing-lease cattle herds look almost benign. Their sharp solid hooves do more damage than the cloven hooves of cattle and sheep — which also came over with the conquistadores.

Interior Secretary Ken Salazar, from a southern-Colorado ranching family, has made politically courageous proposals to bring the wild-horse population into a semblance of control. He's catching predictable hell from wild-and-free advocates oblivious to what huge numbers of horses can do when they are running amok.

Faced not only with the high emotions of horse lovers, but also budget freezes or cuts, the secretary's best short-term hope is only a temporary measure: contraceptive shots. Lured into chutes with hay, the horses can be given injections that appear to be 90 percent effective — for a year. Should studs among their number be gelded? Probably, but that would be at high cost — and no small risk to veterinarians.

Culling the herds and, yes, killing some of their numbers, is among the more sensible solutions. It's also the most heartless, unless you consider feral horses' threats to their four-legged neighbors and to themselves; they're eating and trouncing their habitat to death. The Audubon Society, whose magazine has carried at least two pieces by the acerbic Mr. Williams, the most recent in its January-February edition, is well aware of that grim fact; little by little, perhaps other environmentalists will awaken to it.

More horses could be penned, fed, surgically sterilized and cared for. Proposals to do so offend defenders of free roaming. Sooner or later, though, they've got to face up to worse alternatives.