THANKSGIVING comes only once a year, but turkey farming is a year-T round business. Just ask Ross and Grace Smith, owners and operators of Hillside Turkey Farms in Thurmont, Md. Theirs is one of the very few independently run turkey operations remaining in this area, one where they still raise and process their own turkeys. Hillside is also unusual in that its products are sold directly to customers who want to buy fresh (not frozen) turkeys and out-of-the-ordinary turkey products such as turkey sausage, chipped turkey, turkey bacon, turkey bologna and turkey steaks.

How do people end up as turkey farmers? For the Smiths it meant leaving New York City 10 years ago and returning to the rolling foothills of Western Maryland to take over the family business. The farm itself was started in 1929 when Ross' mother, Pauline Smith, began raising a few turkeys. Admittedly she started out small -- with one turkey. But she took the eggs and raised five turkeys the next year. The next year she raised 100 turkeys, the year after 500. "Then," explains Ross Smith, "My father said, 'Hey, we're making some money in this,' and the next year they went into it together and jumped up to 10,000 turkeys."

Nowadays Hillside Turkey Farms raises 65,000 turkeys a year on a 19-acre farm. Four miles away is its own processing plant and retail store. Thus Ross and Grace Smith are a couple who can really talk turkey.

They'll explain, for instance, that two of the four strains of broad-breasted turkeys they raise -- Cannon and Canadian Hybrid -- are small birds appropriate to the trends of smaller families and apartment living. (They still raise some big birds, Rose-a-Lindas and Nicholas, and the Hillside store sells turkeys ranging in weight from 8 pounds to 42 pounds. The price for fresh, whole turkey is 95 cents per pound; smoked, whole turkey is $2 per pound.)

They'll also explain the importance of having their own farm so that they can control the quality and type of feed. Starting out on a high protein diet, eventually the turkeys are changed to an all-corn ration. "We use a tractor-trailer load of corn every three days -- that's about 900 bushels," Ross explains. "Basically we just give them lots of feed and lots of water."

But what that also means is that the Smiths are sure that their turkeys are not being given any chemical additives or taste-affecting medicines in their feed. They're sure, because they're not adding them.

Owning a turkey farm, though, isn't always easy; there are some factors beyond the farmer's control. There are the minor problems, like the one caused by the helicopters flying around nearby Camp David. Every once in a while the pilots dip down and buzz the turkeys, the Smiths complain, and their several thousand gobblers stampede. (The fact that Camp David buys its turkeys from Hillside is a bit of consolation.) Then there are the medium-size problems, like turkeys being stolen from the buildings and outdoor pens, thefts Ross ascribes to "foxes and two-legged people."

And, of course, there are the big problems, like the streak of record-breaking heat during the summer of 1980. That's when it stayed so hot for so long that Hillside's turkeys began dying from the heat. Finally, they brought 15 firetrucks out to the farm and had them spray the turkeys to keep them cool. Unfortunately, neither the firetrucks nor the tall, specially planted shade grasses provided enough relief. In one day alone, the heat killed 5,000 turkeys. That's a lot of lost Thanksgiving dinners.

By living in the Catoctin Mountains the Smiths have found one of the coolest summer spots around; but, like other farmers, they have nevertheless had to resign themselves to the potential ravages of summer weather. There are other things, though, that they still hope to change. Like the way most Americans cook a fresh turkey. According to them, it's much too long.

"I can't give you the scientific reason why," says Ross, "but if a turkey hasn't been frozen it's more tender and it cooks much faster than a turkey that has been frozen and thawed. My wife can cook a fresh 30-pound turkey in four hours. A lot of people just don't believe that can be true. So for the last few years we've been putting a meat thermometer in with each turkey so that people can check and see that it's really done sooner than they thought it would be."

Not only are many Americans cooking their fresh turkeys too long, according to the Smiths, people are also cooking them upside down. "That's right," Ross explains, "a turkey should be cooked breast side down. Ninety percent of the meat is there, so if that side is down all the juices will run into it and the white meat stays moist."

Ross Smith is also a good source for verifying -- or if necessary, debunking -- various turkey-related myths. Is it true, for instance, that hens are the better choice when roasting turkey? "Well," he answers, "a lot of people will tell you that hens are more tender than toms, but we've never found it so. If you were to put two 18-pound roast turkeys side by side, the hen would have the better-looking breast. But she'd also be two months older than the tom if she were the same weight, and so she wouldn't be quite as tender."

How about the story that turkeys are so stupid they'll stand out in the rain with their mouths open until they drown? Ross Smith shakes his head at that one. "That's an old wives' tale. It's true that domesticated turkeys are unintelligent, but they'd never drown in a rainstorm. What they might do, though, is get scared in a thunderstorm and huddle up and smother to death."

Needless to say, this is Hillside's busiest time of year; the Thanksgiving period is when the Smiths process 1,500 turkeys every day. They're also open seven days a week and have longer hours during the Thanksgiving rush. The reservation deadline for Thanksgiving turkeys is Nov. 22.

Hillside's fresh, whole turkeys are available through several speciality grocery stores in the Maryland suburbs (see the listing below), but calling to reserve a turkey and then picking it up in Thurmont makes for a scenic fall outing. In addition to the Hillside store, nearby Catoctin Mountain Orchards, another family-run business, can provide other ingredients for a Thanksgiving meal. Its November produce includes several varieties of apples, winter squashes and sweet cider, as well as several types of honey, cinnamon honey spread (good on toast) and pear butter.

Directions to Hillside Turkey Farm Store: Take 270 N; continue on it past Frederick, Md. Exit at 15N. Continue to Thurmont, exiting at the intersection of 15 and 550. Take the first left turn (about 1/2 mile) onto Emmitsburg Road. Then take the first right turn onto Elm Street. The store and processing plant will come into view shortly on the left. Store hours are Thursday, Friday and Saturday, 10 a.m. to 3 p.m. Two weeks prior to Thanksgiving, Christmas and Easter the store is open seven days a week from 7 a.m. . . . "until." (It is wise to call ahead and check the hours the day you'll be driving up.) Reservations for Thanksgiving should be made as soon as possible, but no later than Nov. 22. Hillside's phone number is (301) 271-2728.

Directions to Catoctin Mountain Orchard: Stay on (or return to) Rte. 15 going north. The orchard's large roadside stand is several miles past the intersection of 15 and 550, on the left side of the road. Call ahead if you want to find out what specific produce is available: (301) 271-2737.

There are seven grocery stores in the Maryland suburbs where Hillside's fresh and smoked turkeys are available:

Brookville Supermarket, 7027 Brookville Rd., Chevy Chase. 652-2793.

Center Market, 220 E. Diamond Ave., Gaithersburg. 926-0282.

Chevy Chase Supermarket, 8531 Connecticut Ave., Chevy Chase. 656-5133.

Grosvenor's House of Fine Foods, 10401 Grosvenor Place, Rockville. 493-6217.

Potomac Supermarket, 10123 River Rd., Potomac. 299-9300.

Sandy Spring Store, 905 Olney-Sandy Spring Rd., Sandy Spring. 774-4522. Western Market, 4840 WEstern Ave., Chevy Chase, 229-7222