"That jack, he really runs those mares," says Millard Oland, as he bumps his station wagon over the uneven turf of his pastures in Damascus, Md. "I think they're too young for . . . but you never know." He chuckles to himself, a big man with thinning silver hair. "I guess I'm going to have to get my shotgun."

The jack, or male burro, who has never yet had a shotgun shot off over his head (though Oland periodically threatens to do so) is an ambitious fellow, standing all of two feet at the shoulder and intent on pursuing three leggy mustang fillies twice his height.

Now one may well ask what 11 genuine wild horses are doing mere miles from this capital. There are many stranger things in the Maryland suburbs, no doubt, but an enclave of wild horses is still no everyday phenomenon.

Few people in the East have them - there are only about 150 to 200 such animals scattered about. Burt Reynolds, the actor, for instance, a breeder of appaloosas, arabians and thoroughbreds, has two at his 180-acre ranch in Jupiter, Fla., near Palm Beach. And there is a smattering in Pennsylvania, New Jersey, New Hampshire and other states.

But more, probably many more, are on the way. Last month in a local magazine, one could have uncovered a clue buried among the classified ads:

"Every Child At Some Time Or Another Has Dreamed Of Owing His Very Own Pony. Now you can realize this dream. At this moment, the U.S. government is offering a wild horse or burro FREE to anyone who will pay for its capture and transportation. It is also necessary, of course, to be able to provide adequate care for the animal."

In the old days of first piggybanks, puppy fat, and pony worship, one probably would have leaped at the chance. A horse for the asking, and a WILD horse, at that. Or a wild burro - less glamorous perhaps, but cuter.

They're pretty savvy, all right, down at the Bureau of Land Management, a division of the Department of the Interior. They know that with ads such as that one they can count ona good deal of enthusiasm from current members of the "Weekly Reader" horsey set and those who happen to remember belonging. And so, under the auspices of the Wild Free-Roaming Horse and Burro Act of 1971, the "adopt-a-horse" program came into being.

"There are now more than 50,000 wild horses and burrors roaming the rangelands and deserts of the West," says the pamphlet the bureau sends out with every requested application (it's called, as one might expect, "So You'd Like to Adopt a Wild Horse"). And it goes on to explain that mustangs are not native to this country - they were imported by the Spanish to aid in the conquest of the West - and consequently have few natural enemies. Having to compete with other wildlife and with cattle for the available grazing land, their growing numbers present certain ecological difficulties. There simply isn't enough forage to go around.

Before the 1971 act, horse rustling was still a thriving practice on Department of the Interior lands. That served to thin the herds but horror stories ofbrutal mistreatment abound. The "excess" horses, as they are known in government patois have sometimes been shot on sight or slaughtered for pet food.

But various groups have shown a protective interest in the animals' plight all along, and the 1971 act provides for relocation measures and, in some cases, humane destruction of the animals, when foster homes cannot be found.

Some 1,800 horses have been adopted since the program's inception a little more than a year ago, and at least 200 burrors have also found homes. The bureau screens application before holding roundups out West and notifies the lucky parties, who must then hop into vans and pickup trucks and go after their wild charges.

There are presently 4,000 to 5,000 applications on a file at the bureau, says Jim Fox of the Range Office, so response to the program has generally been good. (A similar but smaller program is administered by the Department of Agriculture's Forest Service, which has about 3,600 wild animals on the land it manages compared to the 50,000-plus on Interior property).

Though there is, of course, no purchase price, cross-country transportation for the animals can be expensive, the Bureau estimating that it may cost $400 - if one has to rent a van, for example - to haul a horse from such pickup points as Burns, Ore.; Reno, Nev.; and Susanville, Calif . . . Then, too there is the estimated cost of so-called adequate care to be considered. The bureau intends to enforce adequate nutrition and humane treatment through periodic checkups on year should suffice for proper food and shelter.

Millard Oland sent his 40-year-old son, Dorsey, out to Burns in the autumn of 1974 to pick up four mustangs - a stud, two mares, and a filly. Now he has 11, and another on the way, and says it doesn't cost him and $600 a year to keep each of them.

They roam freely over his 135-acre farm in company with 75 charolais cattle, a few burrors - tame ones, purchased locally - geese and dogs. What with the mares all producing foals last year and the recent arrival of two mustang studs Oland agreed to take when another man responsible for them failed to care for them to the bureau's satisfaction, Oland is on his way to having his very own mustang herd. Under the "adoption" agreement, the bureau retains ownership of the original mustangs and burrors but any offspring belong to the foster owner. Oland hopes to sell the younger horses eventually, though he doesn't seem in any hurry to do so. And while the government-owned horses can't be used for any commercial purpose, he can do what he likes with the foals born under his care.

His son Dorsey thinks he ought to ask $1,000 apiece for the youngsters when they're ready to be sold, but Oland isn't saying what he thinks about that. He justs wants to preserve the breed, he maintains, because of a certain mustang given him to ride when he was growing up - "the best and quickest little horse you ever saw."

Besides, there's a certain tax advantage in adopting a few needy government owned steeds, as he won't hesitate to tell anyone who cares to ask. Oland, who says he had a heart attack and a stroke a few years back and gets around now with the aid of a cane, declares one of his greatest pleasures to be watching the horses he loves grazing and running on the sunny green hills where he's lived for these last 35 years.

"Not very many people around here are interested in the mustangs," he says. "They think it's foolish of me to have'em." He looks out over the little band of shaggy creatures, and adds, "the only pleasure I can get out of them is just what I'm doing right now. See how they eat down in that creek branch? They do that invariably - go down in thebranch and eat all along the edges . . ."