The motorist who drives the length of Maryland Route 28, like the archeologist studying layers of an excavation, sees a society changing from rural to urban.

The old road runs from the rolling farm land around Point of Rocks in Frederick County to the government center of urban Montgomery County in Rockville. There, it crosses Rockville Pike, and darts through the bustling subdivisions along Norbeck Road, coming to an end at Georgia Avenue.

Along its 35-mile length, it passes a store that sells Western boots, farms that sell sweet corn and a shopping mall that sells embarrassingly little.

Route 28 has existed since before the Civil war, and it remained a mud path for years into the automobile age. Robert Perry, who lives at its current northern terminus, Point of Rocks in Frederick County, recalls a drive along the road in the late 1920s.

"Once you left Rockville, you wouldn't see a light until you got up to Dickerson, and then when you got past Dickerson, you were really out in the country."

No longer. A driver heading toward Point of Rocks today may find himself stalled in traffic jams around the county government complex in Rockville before he enters a stretch of road lined with new subdivisions and research facilites.

The lights of urbanization along the Route 28 corridor do not dim until he gets past Darnestown, nine miles out of downtown Rockville.

But thereafter farmland takes over. Once dairy farms lined Route 28, but now there are only a half-dozen left.

"If you could find the truth about it, I expect 75 per cent of the land is owned by real estate firms, doctors and lawyers," said Charles N. Staub, owner of a diner and Western goods store at Beallsville.

Old-timers differ on the influx of new residents and the breakup of the old farms. They realize that the change has also brought wealthier residents and business growth.

"Before all the building, we were rural," said Ace Esworthy, a garage owner in Darnestown. "Now we're practically a city. They've built all around us - subdivision and subdivision. The road here will hardly carry the traffic.

"You hate to see it. I like a little peace and quiet. But I don't have no gripe about it. Because it's time - changing time. Progress, you might call it . . . You'd like to see a little peace and quiet, but it's just not going to happen."

Benoni Allnutt, a Dawsonville farmer who lives several miles off Route 28, looks at the newcomers more pragmatically. Three have bought bits of his farm for homes, and others buy his sweet corn and smoked hams.

"They buy less than 40 acres and build a home on it," he said of the new residents. "They are people working in the District who come out here and buy a place and have horses. Horseback riding seems to be a hobby. We sell them a lot of hay, and that's pretty nice."

But Allnutt has reservations about growth when he contemplates subdivisions in Dawsonville.

"I'd hate to see it," he said, his brow dripping with sweat after work in the fields. He sat in front of his farmhouse and pointed to the horizon beyond his cornfields, adding, "It's kind of nice to sit here and look out. You can see the mountains in Virginia from here."

The major towns along Route 28 date back to the mid-1700s, and many have changed scarcely at all. Some have changed drastically: "Montgomery Court House" is now Rockville.

The big change is in the new subdivisions of the 1960s and 1970s which are often more populous than the towns they settled beside. Their names have a different sound: Flower Valley; Redgate Farms; The Orchards; Ancient Oak.

Figures from the Maryland National Capital Park and Planning Commission show that the population along Route 28 from Rockville to Darnestown nearly tripled from 1970 to 1976, from 10,230 to 29,430. And greater growth, to 34,090, is expected by 1980.

In Norbeck, where the eastern terminus of Route 28 dead-ends into Georgia Avenue, Robert White runs a hardware and lawn and garden supply store. It is on the same spot where his grandfather opened a blacksmith's shop 96 years ago. Now White's 29-year-old son is taking over the business.

White recalls when gasoline was hauled to his store from Rockville by two horses pulling a 500-gallon tank wagon.

"Ninety-eight per cent of them were farmers that came in here before. Now they're all government employees," White said of his customers. "City farmers - they come in here and buy things for their little gardens. They used to buy a pound of beans. Now they buy a couple of ounces."

Like many long-time Route 28 residents, White feels hemmed in by development. But he recently bought a home in the new Flower Valley subdivision on Route 28. He acknowledged that the last 15 years of development has more than quadrupled his sales.

West of Norbeck, subdivisions have replaced farm land and higher-density developments are still being built. In Rockville, Route 28 follows Montgomery Avenue and Jefferson Street, going past the county government buildings and Rockville Mall. The route was moved from the north and east - the road now name Old Baltimore Road - when Rockville Mall was built in 1970 as part of a downtown redevelopment project.

Because of competition and other reasons, the mall has failed to become a major regional retail center. Rockville city planner Thomas Pogue said, however, that 2,000 new government employees from the new county government center to be built just south of the mall, and private sector workers they attract, will help make the mall "a sort of employee-oriented center," serving the downtown Rockville workers.

East of downtown Rockville, Route 28 intersects Interstate 270, the so-called "research belt" of Montgomery County. Gillette, Xerox, Control Data Corp. and Tracor all have large research facilites just off Route 28 and 1-270.

Hunting Hill and Quince Orchard, the first of eight small communities along Route 28 west of Rockville, have been transformed largely because of a single building on a historic estate.

In 1942, Otis Beall Kent purchased the estate of Frederick A. Tschisfely, a Washington wholesale druggist, and consolidated four farms to make a 1,000-acre farm. He built seven lakes, maintained his own fire department and dreamed of such things as a hydroelectric plant on the property.

Kent offered 100 acres of his estate to the National Geographic Society "at an offer we couldn't refuse," according to Melvin Payne, the society's board chairman. The society built a new modern headquarters building on the site and moved 1,200 of its employees there. Payne said the society moved 1,200 of its employees there. Payne said the society moved because of the good offer, the beauty of the site, which includes several lakes and recreational facilities, and the good labor market in small nearby communities.

Urbanization overtook Quince Orchard rapidly."Less than 10 years ago, there used to be an old-fashioned type country general store - where the shopping center sits up there now," said Clifford Bland, 35-year-old resident who runs a nursery and roadside stand across from the Quince Orchard Shopping Center, and just down the road from the new McDonald's hamburger stand.

Bland formerly did construction work, and his last job was building the 166-unit townhouse development behind the shopping center. "They sold as fast as they were built. They started at $30,000 to $40,000 and now they're selling for $50,000 to $60,000 - some for $75,000 or $80,000."

Though he accepts the changes - "It had to come so you might as well say it's all right" - Bland wistfully recalls a quieter time in Quince Orchard.

"When I first came here 35 years ago, you could have horses and ride up and down the road and no one would bother you. I can remember when cars at nighttime would wake you up - it was so seldom that one went by. Now you can't even walk across the street in rush hour."

From Quince Orchard to Darnestown, where Esworthy bemoans the development springing up around him, to Dawsonville, where Allnut still farms but sells hay, sweet corn and smoked hams instead of just wheat and feed corn, to Beallsville, new development gradually tapers off.

Staub's Store is a reminder that the rural past is not yet gone from Route 28. Proprieter Charles N. Staub, sitting at a rolltop desk in the third class post office he runs along with his diner and Western store, noted that two families had recently moved to Beallsville to escape urbanization closer in on Route 28.

Staub's diner is open six days a week, and especially with a fire burning in the corner fireplace in the wintertime it is a popular community gathering place. The Western store caters to residents with horses, for as Staub explained, "Pre'dnear everyone up here has got a horse."

West and north of Beallsville, Route 28 is unquestionably rural.

There are some signs of change. Near the railroad station in Poolesville, a faded sign hangs on a wood-frame International Harvester building while nearby a new white plant displays the modern sign, "Neutron Products, Inc." And while there are no large subdivisions, there are many new houses that indicate larger development may not be far off.

Route 28's northern terminus, where it intersects with U.S. 15, is at Point of Rocks in Frederick County, 25 miles northwest of Rockville.

A passenger who gets off his commuter railroad train and steps onto the red-brick platform of the Point of Rocks neo-Gothic railroad station sees a sleepy small town nestled under a bushy blue-green mountain. There is one modern subdivision, and a few new plants nearby.

But Point of Rocks is a far as one can go on Route 28 to escape urbanization and see the way things once were along the rest of the route in Montgomery County. It is still the country, at least for a while.