Like a bony finger, the peninsula that is Calvert County, 35 miles long and an average of six miles wide, juts into the water between the Chesapeake Bay and the Patuxent River.Cut off from the rest of Maryland, Calvert residents historically took crabs and oysters from the water, raised tobacco on the land and created a rural and independent life style that changed little over the years.

With the dawn of the 1970s, however, a new era came to Calvert County, 25 miles southeast of Washington:

Baltimore Gas and Electric Co. completed a $766 million nuclear power plant at Calvert Cliffs.

The oyster industry, once a mainstay of the economy, all but dried up. Only one of the county's oyster packing plants is still open, and the oysters are imported from the Gulf of Mexico.

The Gov. Thomas Johnson Memorial Bridge was completed, linking the end of the Calvert Peninsula with St. Mary's County across the Patuxent and further eroding the sense of isolation that for centuries had shaped the Calvert character.

A new breed of resident, called a suburbanite, began moving to Calvert in increasing numbers. The suburbanite would neither till the soil nor fish the waters. He would settle in subdivisions that were once tobacco farms, but he would work in or near Washington. He would demand of the county government services the farmers and watermen usually provided for themselves -- garbage collection and recreation, for example. By the end of the decade, the suburbanite would trigger an increase of almost 60 percent in the county population -- from 20,670 to 33,060.

"Calvert County has been the best-kept secret of the Washington area," says Ken Deats, who moved here in the mid-1970s from Prince George's County.

"I wanted to get away from the city to a rural environment, back to the basics where I could have a wood burning stove," said Deats, who came here to sell real estate.

Calvert County indeed may have been a well-kept secret, but it is fast becoming less so. By the year 2000, according to county planning estimates, its present population will be almost doubled, to 64,000.

In 1982, Calvert County is expected to become part of the Washington standard metropolitan statistical area by having a minimum of 15 per cent of its work force commuting to the central counties of the metro area, including Prince George's County.

The designation, constituting formal recognition that Calvert County is a part of Washington's inner orbit, could make it easier for the county to get certain federal funds.

In land area, Calvert is the smallest county in Maryland. It is also one of the oldest. Founded in 1654, it bears the family name of the line of Lords Baltimore, colonial proprietors of Maryland.

In the early 1600s, Capt. John Smith sighted the famous Calvert Cliffs, site of one of the world's richest deposits of marine fossils from the miocene era -- 15 million years ago when most of Maryland east of Washington was under water. In the last ice age, hills of sediment containing the fossils were left behind as sea level fell when vast amounts of ocean water were locked into the polar ice caps.

Then when the ice caps melted, 10,000 years ago, the Susquehanna River overflowed to produce the Chesapeake Bay. The waters of the bay carved out the cliffs, then cut away at them to expose the fossils.

Since Smith sailed up the Chesapeake from Jamestown, change and growth in Calvert County had been slow and gradual -- until the 1970s.

"Calvert County is changing in many ways, at an accelerated rate," said the county planning commission's annual report for 1979.

"An agricultural economy is being swallowed by developments housing people who sleep here and work in metropolitan Washington. The average biennial increase in population is greater than from 1860 to 1950 . . . The total assessable (tax) base increased from $87 million in fiscal year '71 to $158 million in fiscal year '75 to $819 million in fiscal '79 . . ."

Because of the county's proximity to Washington, observes Mary D. Harrison, president of the board of county commissioners, "as long as land is available, there will be people who will purchase it."

It is true, says Harrison, that the new subdivisions are straining the county government. "Suburban subdivisions do not support themselves," she said.

"When you live on a 100-acre farm, you can burn trash in your backyard. If you live in a subdivision, you have to have your trash picked up."

To offset the cost of services to the subdivisions, Harrison is actively trying to recruit more business and industry to expand and diversify the county tax base.

Baltimore Gas and Electric's nuclear power plant, where twin nuclear reactors have been producing more than 10 billion kilowatt hours of electricity since 1977, pays more than 60 percent of the county's real estate taxes. But the county is already getting the maximum it can expect from the power company, said Harrison, and it needs to attract other industries.

"I don't see this as a problem that can't be solved, but it is something we have to work on," said Harrison, 62, a lifelong resident of Calvert and the owner of a retail lumber business. "It isn't just going to happen."

By the same token, she noted, the tide of immigrants to the county has brought new opportunities.

Since the mid-1970s, the Baltimore Symphony has given a concert every fall in the auditorium of Calvert Senior High School.

"Fifteen or 20 years ago that would not have been possible. There were not enough people here to support it," said Harrison.

Two years ago, the county opened a new, 112-bed hospital financed by $8 million in county bonds. With the hospital and its up-to-date medical equipment has come a variety of medical specialists -- cardiologists and orthopedic surgeons.

There is an active artists' guild, a new center for senior citizens and down in Solomons, at the tip of the Calvert peninsula, a marine museum reflects the nautical history of Calvert County.

This summer Ralph Eshelman, director of the museum, will lead diving expeditions in the Patuxent in search of the wrecks of American warships sunk during naval engagements in the War of 1812, when the British sailed up the Patuxent to Prince George's County, marched into Washington and burned the Capitol.

The museum is also restoring the old J. C. Lore oyster-packing house, which operated in Solomons from 1888 until it closed two years, ago with the depletion of the oyster beds.

Originally known as Johnson's, Bournes Island and Sandy Island, Solomons was named after Capt. Isaac Solomon who established the first large-scale commercial oyster-packing plant there in 1859. The oyster industry peaked between 1890 and 1920, and a thriving shipbuilding business also flourished at Solomons. Since then, both industries have seen hard times, but the county continues to attract new people.

"I can go from the Washington D.C. line to my home, and I only hit two stop lights. That's a distance of 60 miles," says Eshelman. "Sure, you're always going to get the people who say, 'I live here now. Let's put up a gate so we don't loose the rural quality of our life.'"

County Commissioner Pete Grover adds, "We see people living here who are living here by choice, not because they were born here. That tells me it must be a prety good place to live."