Three miles west of the Chesapeake Bay, Robert Trott, 83, a lifetime resident of Calvert County, has grazed cattle and grown tobacco on his gently rolling 165-acre farm since he bought it in 1925 for $3,500.

From his two-story farmhouse, which was picked from the pages of a Sears Roebuck & Co. catalog and cost $2,000 to build, Trott can look past his Japanese weeping cherry tree to rows of freshly planted tobacco plants, the barns the plants will dry in later this summer, and a family of mallards swimming on his one-acre pond.

In another direction, Trott can look past his black-eyed Susans to the 75 acres he sold for $60,000 in 1969, on which has sprouted Parran's Wood, a subdivision of 12 custom country homes ranging in value from $75,000 to $250,000.

The fate of the Trott farm illustrates Calvert County's accelerating conversion from an undeveloped and relatively poor county of farmers and fishermen to an expanding bedroom community of commuters bound for jobs in Washington, Baltimore and Annapolis.

"I don't want to see it grow too fast, but I think the development is good--it's progress," said Trott, known by some of his neighbors as the patriarch of Parran's Wood.

Trott's words reflect the views of other county residents, who hope their county can retain its country flavor despite the residential influx they say is inevitable in a sparsely populated county of 37,000 surrounded by more than 5 million people.

And officials of Calvert, Maryland's second-fastest growing county, hope that despite shrinking tax revenues, the county will be able to provide the schools, hospitals, streets, lights, sewers, police and firemen its anticipated residents will need.

The economy of Calvert County, nestled in Southern Maryland and pinched between the tidewaters of the Chesapeake Bay and the Patuxent River, long has been as simple and accommodating as the life style of the people who live here.

Surviving on tobacco harvested from their fields and seafood pulled from the waters, residents of the economically depressed county have for generations regaled in the archeological riches and natural splendor of their untouched 140,000-acre peninsula 35 miles southeast of Washington.

But in 1975, atop the soaring bluffs of lower Calvert County, officials of the Baltimore Gas & Electric Co. (BG&E) pulled the switch on the new $778 million Calvert Cliffs nuclear power plant, sending 1,680 megawatts of electricity to BG&E customers throughout central Maryland.

Although almost none of the electricity goes to Calvert residents, the twin reactors overlooking the bay immediately began pumping millions of dollars in taxes into the county treasury, jolting it out of economic primeval times.

The BG&E revenues triggered an unprecedented boom in Calvert in the mid-to-late 1970s. The county constructed three schools, two hospitals, three regional parks, repaved most of its roads and built a bridge across the mouth of the Patuxent.

"Construction of the nuclear power plant provided a lot of jobs and created a tremendous tax base relative to what had existed before," said attorney Thomas Axley, chairman of the division of economic development of the Calvert County Chamber of Commerce. "We were a poor county before the plant, and with its revenues we were able to develop the amenities that hadn't been provided in this county for many years."

Meanwhile, the county's population was increasing by 67 percent to 34,638, giving it, according to the 1980 census, the state's second-highest growth rate during the 1970s and touching off another local industry--home building.

County planners expect the influx to continue into the next century since 70 percent of the land in Calvert is agricultural and available in the form of moderately priced three-to-five acre parcels. Much of it is within commuting distance of Washington, Baltimore and Annapolis.

Already almost half of Calvert's workers commute to work outside the county, doing much of their shopping beyond its borders as well, data provided by the county shows.

The conversion from farming and fishing to a commuter society has sparked concern that revenue from the nuclear plant will be insufficient to support the bedroom community developing here.

Joe Allman, the county's director of administration and finance, said the strain is beginning to show. The county, which has enjoyed a robust surplus in recent years, had to draw on almost $2 million of its anticipated $5.5 million surplus to balance a $31.5 million fiscal 1984 budget.

While the surplus keeps the budget in balance next year, Allman anticipates rough years ahead, as revenues decrease from the county's two top taxpayers--the nuclear power plant and the Columbia-Consolidated LNG (liquefied natural gas) terminal three miles south of the BG&E plant, along the Chesapeake.

In 1978, the terminal--the largest in the nation--took in its first shipment of liquefied natural gas, with the expectation that long-term contracts to buy Algerian natural gas would make it one of the busiest gas ports in the world and serve as another large source of revenue for the county.

But the LNG terminal has been idle for two years and faces an uncertain future because of a long-simmering dispute over the price of Algerian natural gas.

In addition, tax payments from BG&E are expected to diminish as the value of the power plant is depreciated. Local business people say there is no guarantee that the nuclear plant won't shut down, as many have in recent years, or that when the current one wears out, it will be rebuilt.

"What's happening is that if we don't find some way of reducing our dependence on the tax revenue from the power plant . . . and a new plant isn't constructed, then we're going to have terrific problems down here," said Harold Kahl, vice president of Calvert Bank.

With most of the new development in the county residential rather than commercial or industrial, expenses are surpassing revenues, he said. "Houses provide demand for services that are far more expensive than they return in the form of tax revenue," said Kahl, referring to schools, hospitals, streets, lights and sewers.

"It's increasingly important that we develop the commercial side of the tax base down here to offset the residential expenses, or our property tax rates are going to be so exorbitant no one will be able to live here," Kahl said.

With revenue sources decreasing, the county for the past year and a half has been trying intensively to promote economic development in light industry and tourism, said finance director Allman.

The county commissioners held an economic development summit 18 months ago. That led to a task force and the formation of a county office of economic development.

The first task for Talmage Reeves, director of the county's new development office, was to market the Calvert County Industrial Park, which had been lying undeveloped and unpromoted since 1965.

The industrial park, a 226-acre site near the county seat of Prince Frederick, has been designated one of the state's six enterprise zones, Reeves said, which allows the county to offer credits on state and local taxes. Today, while some businesses have been attracted, much of the park lies vacant.

Calvert County's Board of Commissioners last Tuesday approved a new comprehensive plan that seeks to encourage commercial growth while safeguarding the county's rural character.

The plan would create seven town centers in the county, four large and three small, where zoning restrictions would be loosened and growth of commerce and light industry would be encouraged.

Residential development in rural areas will still be allowed on parcels averaging five acres, and heavy commercial development will be concentrated in less than 10 percent of the county, planners said.

Attorney Axley: "There had been a real feeling in the community as recently as three years or four years ago that the best thing you could do for the county was to put a gate at the northern end and not let anybody else through.

"Now they're recognizing that through the town center concept we can keep our county country-like and allow for the development that's needed to pay for it," he said.

"The county could afford not to be friendly to businesses five or six years ago because it had all the tax revenues it wanted, but that's not quite true anymore." CAPTION: Map, By Dave Cook--The Washington Post; Picture 1, Robert Trott, 83, a lifetime resident of Calvert County, in front of new homes built on part of the 70 acres of land he sold in 1969 for $60,000; Pictures 2 and 3, The Calvert Cliff nuclear power plant, above, was built in 1975 and is a top source of revenue for Calvert County, enabling it to build schools, parks, and hospitals. Farm workers rest on a truck bed after a day of planting tobacco. Photos by Vanessa Barnes Hillian -- The Washington Post