Robert Colinus didn't really intend for his 600-acre quail heaven to be a one-man operation, it just worked out that way.

"I was over 50 when I started this thing," he said as he showed a visitor around the rolling, wooded Loudoun County tract. "I didn't know much about farming or landgrading, so I tried to hire people.

"I hired a man to clear for me. Half the time he didn't show up and the rest of the time he didn't do what I wanted, so I bought this," Colinus said, patting a well-worn D-6 Caterpillar bulldozer. "It took a while to learn how to run it, but it's fun."

He fired up a big green John Deere tractor to show the tricks the hydraulic scraper could do. "I thought the local farmers would be happy to make good cash money plowing and planting for me, but that didn't work out, so I had to learn how to do it myself."

So for nearly two decades, almost every weekend plus every other day he can slip away from the office, the 69-year-old Arlington realtor has cleared, graded, plowed and planted whatever he knows or has been told will attract, feed and shelter quail.

Quail need seeds to eat, thickets to hide in, tall but open grass to roost and nest in and woods to escape to when pressed by predators, including Robert Colinus, who hunts them every day he can during the season.

It is nothing like a shooting preserve, where pen-raised birds are put out in the morning to be shot in the afternoon. Colinus' birds are wild, and so well provided with food and cover that he never knows when, where or if his dogs can find them. in a full day's hunting last week, for instance, he and a guest saw but two birds; they did not shoot at one and missed the other.

He doesn't know nor care to guess how much time and money he has spent on the place: "This is my hobby. To hell with the cost per quail, I love this land and enjoy working on it." He threshed a buckwheat head between his hands and winnowed the chaff with a puff of breath that left several dozen seeds in his palm. "Look at that: This is the kind of long-lasting grain they need to carry them through March and April."

Mixed with the buckwheat was bicolor lespedeza and German, Japanese and Proso millet. Other clearings are planted to corn, wheat and soybeans. Thickets of autumn olive, established on the advice of experts, provide cover, although Colinus has never found a single olive seed in a quail's crop.

"The turkeys love 'em, though, so it wasn't a waste of time," he said.

The plantings cover more than a hundred clearings, averaging an acre in size, dotted throughtout the tract. Each is bordered by woods and thickets, so that a feeding covey need never go more than a few yards from cover. "It grows too thick for ideal hunting because I use four tons of lime per acre plus fertilizer," he said. "I don't care so much about whether I can find the birds, as long ass they can find what they need."

It's all done for love of quail; there are no financial benefits except that the land qualifies for the conservation land-use category, which slightly reduces his taxes. He doesn't entertain business clients and he has no plant to immortalize himself as a philanthropist by leaving the land to the public, although "I do worry about what's to become of it. Maybe I'll find another quail nut.

Actually, I'm a small-timer. There are people who keep thousands of acres exclusively for quail, or who will spend $50,000 a year on a piece of ground on the Eastern Shore just for their own private goose shooting. If I had that kind of money I probably would do something else with it, although I can't think of anything I'd rather do than work this place."

What kind of money Colinus does have is his own business, but there plainly is plenty of it, "a lot more than I ever thought I'd see when I was growing up down in southern Virginia." He came to Washington during the Depression with a friend who had some busines here, and dropped by the Washington Gas Light Co. to see if there was a job to be had. There wasn't, of course, but he left such an impression that an offer came in the mail three months later.

His career was interrupted by World War II, and afterward he tried his hand at one thing and another, including fixing and selling junked cars. Soon he was selling hundreds of cars a year to dealers hundereds of miles away. Eventually he switched to real estate, of which he has bought and sold a great, deal even if you don't count "the farm," as he calls it, which was assembled from 18 different parcels.He's still active in the business, and one of his favorite things about the farm is that there is no telephone. Associates have learned to leave messages for him at the general store where he picks up his brown eggs, and at the service station where he buys gas for his canary-yellow four-wheel-drive Chevy.

It is conventional wisdom among wildlife experts that trying to create quail habitat is never practical and seldom works. Colinus agrees that it costs like hell even when the labor is free, but nobody can tell him it doesn't work. "I usually count about 60 coveys here in the fall," he said. "When I started, I doubt there were more than three." Since a covey averages about 15 birds, the farm is regularly supporting more than a qauil per acre; land that habors a covey per 100 acres is considered good quail country.

"I've had experts come here and tell me there's food and cover for three of four birds per acre, but I think the land area is the controlling factor. I believe quail are territorial, and that a covey that feeds in a particular place will drive others away. It is said that a quail is hatched, lives and dies within a radius of 700 yards."

Colinus reads everything he can find on quail and land managment, but has learned to trust his own observations and experience. He carefully distinguishes between what he knows and what he has read or has been told. He is not an educated man, he said more than once during a splendid day of going over the ground, but it has become clear to him that a lot of what passes for wildlife knowledge is nonsense.e.

"I went over to a famous shooting preserve on the Eastern Shore once to see what I could learn," he said. "They had three fulltime wildlife biologists, a huge budget, and the head of the outfit is crazy about qauil. I listened to those boys for a while until I came to find out the best they could do was 22 coveys on their 3,700 acres. Then I came home, and ever since, I've been wondering what it is they teach those boys in college."

What's good for quail is good for many other animals. Colinus has geese, ducks and beaver on his ponds, hosts of songbirds in his woods and fields, great droves of turkeys and grouse, and deer that leave pony-size hoofprints. He also has owls, hawks, foxes, skunks, weasels and other predators that wax fat on quail at his expense, enough of them to keep a local trapper busy.

It is in fact a wildlife paradise, an island of plenty in countryside that is fast being engulfed by Washington's exurbs. "Virginia recently gave him a conservation award, but he asked them to slip it under the table, because he didn't want to attract attention.

"I had no end of problems with poachers when I started out," he said. With the help of the sheriff and the game wardens we finally convinced them that they couldn't get away with sneaking in on me, and the last thingk I need is for a whole new bunch to find out about this place."

Colinus hunts quail only. He will take the odd turkey or grouse he comes across in season, but he never goes looking for them. He doesn't hunt deer, although he knows there are too many on the place. He wishes he could let others hunt on him. but "I have tried it enough times to know it just won't work. Old friends of mine -- used to be friends of mine -- have promised me one thing and then have come here and shot up whatever they pleased. I give permission to one man to hunt by himself and he starts bringing in friends by the carload. It makes me feel bad, selfish, to keep it to myself and people who shoot with me, but I just had to give up trying to be nice."

The lament is persuasive, because Coninus seems naturally open-handed: Anyone who tries to grab a lunch check from his is likely to get his knuckles rapped.

He is more than a little proud of the place and delights in showing visitors around, especially those who want to learn how to encourage wildlife on their own land. But he asked a reporter to take no pictures ("You could spot that pond easy on a topo map")) and to disguise his identity ("Ain't that a hell of a note, an honest man having to hide his name?"), which has been done. CAPTION:

Illustration, no caption, By Stuart Armstrong.