A century ago, Baltimore was "the city" to people in Calvert County, a 50-mile-long strip separating the Patuxent River and the Chesapeake Bay. But these days, Calvert finds itself linked increasingly and inextricably to Washington by a large and growing commuter population.

"Just to show you," said Fran Tracy of the county Chamber of Commerce, "we don't even have a major road into Baltimore. It's two lanes that way and four lanes into Washington."

The trend is pronounced enough that as of next month the U.S. Census Bureau will place Calvert in the Washington Standard Metropolitan Statistical Area, an event considered not insignificant by folks who have never been in anybody's SMSA before.

So it was with great consternation that county residents greeted the news, learned last month, that American Telephone & Telegraph's court-approved divestiture plan to take effect Jan. 1 calls for lower Calvert to be permanently linked by telephone grid not to Washington, but to Baltimore. The northern third of the county would retain its local dialing privileges to Washington by virtue of an exception to the new map approved by the court, but residences and businesses in the lower two-thirds fear they will lose their crucial direct link.

A direct mail company president calls the idea "crazy." The head of a real estate business says it will be "disastrous." And the local representative for a statewide drafting firm says if it goes through, "We might as well throw our $100,000 computer out the window" because there will be no phone link to run it on.

Their concern is twofold.

Immediately, there is worry about the lower county's potential loss of direct, local-dialing access to Washington on the 855 exchange. Currently used by 350 lower-county customers, 855 is a lifeline for some businesses and a comfort to residents who work or have families in the D.C. area.

Long-term, the fear is that the decision could stamp budding Calvert forever in the minds of Washingtonians as a "long-distance" area, slowing development and diverting potential settlers to areas where communications are better.

The conflict arises over Chesapeake & Potomac Telephone Co.'s decision to place Calvert in the Baltimore "local access transport area (LATA)," with phone connections through Annapolis. At the same time C&P put Calvert's sister Southern Maryland counties, St. Mary's and Charles, in the Washington LATA.

Under the divestiture agreement the entire nation will be broken down into LATAs. Local phone companies will handle calls within a LATA, but calls crossing LATA boundaries must be carried by a long-distance carrier such as MCI, Sprint or AT&T long lines, unless an exception is granted in high-use areas.

C&P won the exception to continue to offer local 855 dialing from northern Calvert into the Washington area. But the lower two-thirds of the county was not excepted, and the way residents and businessmen from Huntingtown south to Solomons see it, that leaves them in limbo, out of local touch not only with Washington but with their neighboring counties across the Patuxent.

"We'd much rather be providing foreign exchange and toll service across the state," said Lynne Troup of C&P, "but the divestiture agreement calls for these LATAs, supposedly for the benefit of the consumer. Well, you can see how much good it's going to do the consumer."

"The way I understand it, as of Jan. 1 the 855 exchange is gone," said Kirk Swain, president of Direct Mail Lithographers in Prince Frederick. It would savage his business, he said.

Swain moved his 130-employe plant here from Northern Virginia two years ago but still gets almost all his trade from the D.C. area. He takes orders on eight 855 exchanges and estimates that 8,000 calls a month go in and out on the lines. Linking to Baltimore, he maintains, makes as much sense as "linking us with Altoona, Pa."

The prospective loss of local Washington dialing is no less a concern to some private residents, many of whom wrote to the chamber to protest. "Our 855 telephone line . . . is our essential connection to our doctors, pediatrician, dentist, my work and last but not least our friends and family," wrote William DeBoard of Huntingtown.

As volunteer coordinator of the county's effort to reject the Baltimore link, Tracy has petitioned the judge in the divestiture case, Harold H. Greene of the U.S. District Court in Washington, to alter C&P's map and put Calvert in the Washington LATA.

"Judge Greene said emphatically in his ruling that it was not the intention of divestiture to discontinue or disrupt any service," said Tracy, who moved here from Prince George's County and who has only an 855 D.C. line at home. "The intention was just to change the provider."