Ralph Timmons pulled his car off the road and rumbled across a field of fledgling wheat. At the bottom of a slope he stopped at a low mound of dirt and gravel at least 100 feet across.

"Looks like somebody just dumped 10 or 15 truckloads of gravel here," he said. "Well -- they didn't."

Up the slope, the U.S. Soil Conservation Service agent was up to his waist in a gully hewn by rain. The gully twisted like a dried creekbed up into the wheat. Timmons scraped up a handful of powdery topsoil: Tons of this, he said, had washed down to a nearby creek and out to the Chesapeake Bay. Only the heavy gravel was left behind.

About six tons of soil washes off each acre of Maryland cropland every year, scientists calculate, and much of it ends up in the bay and its tributaries. With the soil comes27 percent of the phosphorus and 60 percent of the nitrogen that enters the bay in an average year. The chemicals are two of the most harmful pollutants entering the nation's largest and most productive estuary.

An acre of town houses will pollute more than will an acre of farmland, conservationists say, but Maryland has 2.3 million acres of farmland, or 38 percent of the state. Just 12 percent, or 763,000 acres, is urbanized. That makes cropland, along with sewage plants and shoreline development, a serious problem.

The runoff soil chokes clam and oyster beds in the bay. The fertilizers spawn the rapid growth of algae, which block sunlight and kill underwater plants. The decaying plants, in turn, rob the water -- and crabs, oysters and other marine life -- of sorely needed oxygen. Between 1950 and 1980, according to the U.S. Environmental Protection Agency, the area of the bay with no dissolved oxygen at the bottom increased fifteenfold.

This is one of the strongest reasons, scientists believe, for the bay's declining productivity. During the past 20 years the annual oyster harvest fell from 30 million pounds to 20 million pounds. Commercial harvest of striped bass, or rockfish, fell from 6.7 million pounds to1.9 million in the last decade, prompting a state ban on rockfish fishing imposed this year.

This new knowledge of the amount of damage that eroded soil can cause in the bay has changed the job for Timmons and his colleagues: Once they were fighting to save the soil from the ravages of water; now they are fighting to save the water from the damage wrought by soil.

In recent years, Timmons has begun persuading Kent County farmers to give up their time-honored plows that, he explained, expose the soil and shake it loose. He has helped them build ponds to silt out the soil before it reaches creeks, and build terraces and long, grass-planted drainage ditches to filter the soil from the water.

Kent County is on the edge of the bay, surrounded by rivers and laced by creeks. State officials say farmers here are practicing soil conservation with a fervor unmatched elsewhere in the state.

They have abandoned plow farming on more than 13,000 acres since 1980 and have covered 237 acres with grass waterways. They have built more than 50,000 feet of terraces and diversions and 137 ponds.

When Timmons came to work in Chestertown 11 years ago, he recalled: "We weren't thinking about what was happening downstream . . . . Eleven years ago, no-till farming was just getting started. About 80 to 90 percent of the farmers were using conventional methods."

Now, Timmons estimates that well over half the county farmers are using no-till methods, in which seeds are inserted through the soil on a slim metal disk and the surface of the soil is left undisturbed and protected by the remains of the previous crop.

A higher proportion of Maryland farmland is planted with no-till or other conservation methods than land in any other state save Delaware. According to the U.S. Soil Conservation Service -- which gives much credit to a cost-sharing program introduced by the state two years ago -- soil erosion in Maryland was reduced by about 600,000 tons in 1984 alone. That, according to the service's calculations, is enough to fill dump trucks stacked 80 high across the entire span of the Chesapeake Bay Bridge.

George W. (Butch) Weidenmayer is one of Timmons' star converts. Twenty years ago, when Weidenmayer and his father started farming at Kennedyville, on the edge of Urieville Lake a few miles east of Chestertown, they used traditional farming methods like other farmers around them.

In the years since, their soil washed away. Acres of lake silted shut and algae grew out of control.

"I've seen gullies open up in one rainstorm, so bad you couldn't drive across them," Weidenmayer said. "The soil is very fine. It liquifies. It's like chocolate milk running down the hill."

Now he uses no-till farming for most of his crops. He is planting his crops along the contours of the land. Last year he finished his grass waterways. He put in two ponds to catch the silt, and he recently installed terraces to steer the water toward the waterways.

"I always was a conservationist," said Weidenmayer, who reckons he has virtually eliminated soil erosion on his land. "Now I'm a superconservationist. It's good for the pocketbook, it's good for the land. It's good for everybody."

Weidenmayer admits that he was skeptical until he converted. But now he says that conservation farming saves him money: It saves him the time and fuel he would have to use plowing his fields and, because his soil stays put, he does not lose expensive fertilizer.

But farming is steeped in tradition, with skills handed down from father to son, and ways change hard. So Timmons goes on his rounds, combining the fervor of the evangelist with the determination of an insurance sales person.

"You have to be careful not to offend people," Timmons said. "You can't tell them that everything they've been doing for the past 20 years is wrong. But you do have to sell conservation -- once you've got your foot in the door."

"You're doing what you know in your heart is right," he added. "You are only the steward of your land for a little while. You want to pass it on to the next generation in a little better shape than you received it."

More often than not, Timmons said, getting his foot in the door means convincing farmers to build ponds to catch soil runoff -- or a "waterfowl preservation area," as they are described to the tax collector. If he can sell a farmer on this, Timmons said, he generally has him sold on the whole works.

Before long, Timmons explained, the farmer finds his pond is silting up; then he gets interested in no-till farming and grass waterways.

"A lot of us are reluctant to change," Timmons said. "If someone tries, he'll try on the worst piece of ground he has. A lot of the farmers are geared up to the old ways . . . . But most of the farmers around here are very conservationist-minded."

"Remember this," said Alan Stradley, president of Kent County's Farm Bureau. "A farmer is interested in trying new things and trying to be progressive. He wants to conserve his soil as much as anybody else does. That's what really started it."

Stradley, who farms near Chestertown, feels that farmers are being used as scapegoats.

"Farmers get blamed for the problems of the Chesapeake Bay, when it's really not all their fault," he said. "When you take Baltimore City, with their vast areas covered with macadam and concrete, and all the spillage of everything and anything that washes into the bay -- it takes an awful lot of farmland to outdo that."

"Agriculture: It's been around for so long that people just didn't think of it as a culprit," said Steve Bunker, a scientist with the Chesapeake Bay Foundation, a nonprofit education and conservation group in Annapolis. "What we are seeing now is that there are twice as many reasons for soil conservation as we realized before."