Two hundred years ago, when the Dades' farm still belonged to their ancestors, the Simmonses, it was called "New Laid Tomahavik," for reasons no-one can remember. Then the name "Mountaintop," supplanted that - more descriptive of the 1975 acres that crawl halfway up one of the Catoctin mountains in southern Frederick

In a few years, however, it may be called "Hilltop Heights," or "Jefferson Acres," and those fields may be dotted with new homes, driveways and tricycles. Or it may be fallow, an in discriminate tangle of brush that passers-by could call "the old Dade place."

It was last fall that Maurice and Hazel Dade decided they had to sell the farm. Both in their 70s, they didn't want to handle the chores of keeping up the fences, the buildings, and the land, in the rural area of Jefferson, Md., 50 miles north of Washington.

For health reasons and for financial reasons, the Dade's two children can't move in and take over. The neighbor who has rented the land for the past 20 years to farm his own herd of diary cows has told the Dades he just doesn't want to buy right now.

Despite changes in the federal tax laws designed to help farmers, despite both existing and planned state legislation designed to preserve agricultural land, more and more farms are slipping away from the families who have long owned and worked them. The land now supports homes, or industrial parks, or it falls into disuse while waiting for some sort of development. Every year, more than 35,000 acres of farmland in Maryland stop being farmed and become something else.

Federal tax reform measures passed in 1976 make it easier - and cheaper - for people like the Dades to pass the farm along to their children. Proposed state legislation would give them a chance of selling the development rights to the state, ensuring that the land would be kept as a farm forever.

The work would still be there. The work gets harder as the farmers get older. And the children often have other things to do.

"Often," said a legislative aide familiar with the proposed Maryland bill and the arguments around it, "the farmers don't want to admit that their kids just don't want to be farmers."

The Dades don't mind admitting it. Their son Stanley, 40, "loved to farm," but a bad back and a severe allergy to hay prohibited it, so he became a postman in effJerson instead.

"He tried and tried," said Dade. "He loved it, but he couldn't."

Their daughter Joyce, 45, is a widow with three daughters and a grandchild of her own, is in no position to take over the responsibility, even if the lease arrangement were continued.

So six weeks ago they stuck a "For Sale" sign out by the road. When a buyer comes along, they're going to move two miles down the road into the town of Jefferson. They won't come back by the old place too often, especially if they know the fields have gone fallow.

We don't want to see it go down," said Mrs. Dade.

Still, she and her husband know the cost of keeping it is too high for them. "The children are anxious for us to sell and take it easy," he said. She added, "We're right here. We see what has to be done - there's so much. There's too much upkeep to the buildings and grounds. Come summer, it's mow, mow, mow."

"It's a burden," echoed Maurice, who pronounces his name "Morris."

Their asking price is $2,000 an acre for the 175 hilly acres, the main farmhouse, the grain silo, the barn, the outbuildings, and the house Maurice's father built for the couple in 1931.

"We've been studying on it [selling] a year or two," said Maurice. Now the couple has become resigned to giving up the farm, and they are anxious to get their asking price anxious to show off the sweep of fields hiding behind each other in great receding rolls.

The Dades care what will become of the land, but they don't see the point in caring. "It's in the hands of ar ealtor. If he brings someone here, as long as the someone has the money, I couldn't have any say in what happens," Maurice said matter-of-factly. "That's it."

"Are the Dades typical?" mused a state senate aide familiar with the problems of farmers and farmland preservation. "Sure. Their land's their pension. They want to cash in their pension."

The Dades present a similar argument; selling makes sense, they said. There are, however, gaps in their posture of practicality. They start to muse as they sit in their living room, walled in by pictures of children, grandchildren and their one great-grandchild. They muse, too, when they look out their dining-room windows toward the Blue Ridge Mountains.

Mrs. Dade looked out for a moment, then glanced over the closer landscape of picture, sofas and cushions inside. "You can't live on the view," she said. But then her gaze sneaked back outside, and her finger pointed to the gap between the distant mountains where Harper's Ferry sits. "For a few days in - let's see - October and March, the sun sets right in there, right in the gap. That's pretty."

"Yes," Maurice said, "there is some sentimental value to the farm. You can't charge for that, though. One part of me wouldn't sell it for anything." He pulled out the family history album with its account of his great-great-great grandfather, Col. Robert Townsend Dade, who married a Simmons girl then took over the Simmons farm.

He remembered his grandfather, with stories about the 40 slaves who once lived on the place, with stories about the rebel army camping down by the road during the Civil War - "right down in that field."

He remembered growing up there with his brothers - since gone on to other things - his parents and his grandparents. "Grandma had one of those ear trumpets; it came out to here he held a hand a foot from his head.

The family feeling still carries down. When Dade's 13-year-old grandson Joe, Stanley's son, first saw the for sale sign, he ran home, laid down on his bed and cried his eyes out," Hazel Dade recalled. "He comes up here all the time. He loves the place."

She paused. "Sure, we'd like to wait and see if Joe'd take it over," she said. "But he's too young yet to judge. And while he's getting older, we're getting older." The other grandchildren on't seem to have Joe's interest, she said.

"It's very difficult for young people to get into farming," explained Jack Miller of the state Farm Bureau. "It's very difficult to get land; even if you have the land, there's the cost of equipment. You need money to start with. You can pay $15,000 for a tractor."

Most of those worries at the Dade place now fall to Richard Hawker, the man who rents the acreage from the Dades and farms 17 dairy cows, sending 500 gallons of milk a week to Washington area dairies. Hawker pays $800 a month in rent to graze his cows and raise the hay and grain to feed them a low price for the acreage but, "He's like a son to us," said Maurice.

However Hawker, who also rents an adjacent farm, is nearing 50 and doesn't want to be saddled with mortgage payments, the Dades say. He just doesn't want to buy. And with the farm's upkeep costs, with its annual tax bill of $1,500 and with its worries, it just isn't worth it for the Dades to stay on.

"I suppose if anybody buys this farm they're going to develop it," Maurice said, as he walked up the rutted driveway toward the old farmhouse where "Dickie" Hawker lives. He pointed up the hill to the treeline; the light bark of a lone birch marks the spot where the Dades' spring originates, giving the two houses on the property their water.

"I ride around the county and see some beautiful farms developed," he said, turning back to the house. "It's sad." The fringes of development in exurban Washington are getting closer to the Dades'; a dozen new houses are being built on an adjacent farm, which was recently sold.

"Development is all around me . . . I haven't got any more mixed feelings about selling and having it developed. I just don't want to see someone taking it then selling it for double the price. But that will probably happen," he added.

Nonetheless, "if we can find a buyer, we'll sell," Maurice said. Hazel Dade smiled and shook her head slightly. "You can't live on sentimentality alone," she said in a soft voice.