It deserved its own dateline, so removed from the metropolitan mainstream was the seat of Prince George's County in 1976 when I first arrived on the scene. Only 20 miles from bustling downtown Washington, Upper Marlboro (known to residents as Marlboro) was a small town where county employes sick of eating vending machine lunches at their desks hungrily yearned for a pair of Golden Arches. They even sent petitions to McDonald's--to no avail.

There were, then, 646 year-round residents, plus several hundred daytime inhabitants, most of whom worked for the county. The seat of government was the courthouse, for all branches of government. Over by School House Pond, the incongruously modern-looking county administration building, bearing a strong resemblance to the Kennedy Center, was taking shape but wasn't quite ready for occupancy.

It seemed odd that this sleepy place was the capital of the Washington area's most populous jurisdiction, but there it was.

Getting there, it seemed to me at the time, was half the fun. To travel the 10 miles on Maryland Rte. 202 from the Capital Beltway to Marlboro was to pass from the fast lane to the slow one, as suburbs yielded to country astride a narrow, two-lane road with soft shoulders.

The shoulders are paved now, and the traffic count is up, along with many new buildings. The little farmhouse at the Beltway ramp is gone, replaced by a huge office center. While signs of the past persist in the remaining rural homes and fields, other signs signal the future--"Coming Soon--Largo Plaza Shopping Center," "Largo Centre--175 acres for office, retail and other uses," "For Sale--42 One-Acre Lots," "Custom Built Homes on Sites 4 1/2 to 11 acres"--almost all the way to Marlboro.

Subdivisions, too, have sprouted amidst the corn and tobacco fields. At Ramblewood, the modest model homes adjoin an old tobacco barn. "The Towns of Kettering" increasingly edge along Rte. 202 opposite the Prince George's Community College and Largo High School, outposts of modern architecture and development when I first drove by.

Opposite the Capitol Baptist Church and Christian Academy, which has added fancy new lights in its parking lot, bulldozers churn the earth for the second section of Largo Knolls, a subdivision of three- and four-bedroom homes priced in the $100,000 range. Eventually, there will be 317 houses, John Lucente, the builder, says proudly.

In Marlboro proper, the changes are at once striking and barely noticeable. The place looks the same, but there are differences of style and substance.

County Council members no longer address each other and witnesses at public hearings and meetings by their first names, as they did in the recent past, except for Frank Casula, the council chairman, who's been around for a while.

The council now meets in the county office building, of course, but it's no longer new. It's so old, in fact, that the new administration is about to renumber and reassign spaces in the adjoining 800-car garage. "People back from the Winfield Kelly administration are still using stickers," said Tim Ayers, aide to Parris Glendening, the new county executive.

On Main Street, meanwhile, the old filling station is a drive-in bank, and Buck's general store has become a law office (making the green-and-white cap I once bought there something of a collector's item, no doubt). For years, the road was labeled Rte. 408. Inexplicably, it is now Rte. 725.

The thoroughfare through town is still a fixture but maybe not for long. Under the long-awaited Upper Marlboro Plan, a brick walkway connecting the county office building and the courthouse is to bisect and partially close it. Who will pay for the pathway remains to be seen. "Others," Glendening says.

The plan proceeds nonetheless, with the completion of the Gabriel Duvall Law Building, the first of many projected. Built by the Kidwells of College Park, possibly the county's premiere office builders, the four-story brick colonial structure with white columns faces the future pedestrian walkway.

It is named after a Prince Georgian of Huguenot ancestry who capped his career with an appointment to the U.S. Supreme Court in 1811.

Underscoring coming changes, the Suburban Bank has just moved into the new Duvall building from the old Farmers and Merchants Bank building. The former office on Main Street was smack in the path of the walkway and thus slated for demolition.

"You know, tear down, put up," observed Billie Hill, who sits at the county administration building information desk and is a veteran observer of the Marlboro scene.

A new state office building, scheduled to go up under the Marlboro plan, will bring several hundred additional daytime inhabitants to the town, where the full-time population grew in the 1970s by 28.2 percent, to 828 by census count.

School House Pond, a five-acre flooded mill stream, has survived all changes hereabouts, while undergoing some of its own. In recent years, it had become a breeding ground for algae and silted in to a depth of two or three feet. The government has spent $709,000 to dredge it to seven feet, deep enough for fish and wildlife.

The "School House Pond Development Project," which will be dedicated Saturday, also includes a one-third-mile-long boardwalk and nature trail, a picnic area and a monument to Prince George's Vietnam veterans.

Eventually, a restaurant, recreational facilities and a tobacco museum are to be built by pondside, under the Marlboro plan. Will this be "Pondplace," Prince George's answer to Baltimore's Harborplace? "It's not quite that stature," said Craig Kellstrom, a county parks department spokesman.

On the other side of town, Rte. 4 is a four-lane divided highway that is the shortest, direct route to Washington, where it becomes Pennsylvania Avenue SE. Without any change in directional definition, the sign people have changed Rte. 4 "East" to "South" and Rte. 4 "West" to "North."

Under the Rte. 4 overpass is the old Marlboro Race Track, which assumed legendary proportions as the focal point in the bribery trial and conviction of former Maryland governor Marvin Mandel. In this town so conscious of its own history, there is no memorial plaque.

The track itself, after some years of disuse, has been turned into the Prince George's County Equestrian Center. It is rented to horse owners and trainers who drive cars and pickups with license plates that spell out things like "HOOF."

"It's away from the races, the excitement. The horses love it," reported Lillian Kuykendall, a 20-year-old jockey who had worried her own career would suffer so far from the action. "But so far, so good," she said. "In the month I've been here, I've gotten 40 mounts."

The equestrian center also will soon be the site of the county fair, which used to be at the Bowie Race Track, where things were getting too civilized.

The Marlboro I once knew also is changing, inexorably, it seems. The modest Marlborough House restaurant in the shopping center next to the racetrack is no more. Completely redone and renamed, it's now CJ's. The courthouse crowd still goes there for lunch, but at night it's a disco.

"CJ's Brings a Touch of Class to the Area," headlined a restaurant review (prominently posted in the entrance) when it opened in 1980. "It exudes a sort of sophistication that draws moderately affluent clientele for lunching, dining, drinking and dancing seven nights a week."

And someday--perhaps it's just a matter of time--Upper Marlboro may even have its own set of Golden Arches.