Annapolis, Md. — I am 50 miles and one state away from home, and in desperate need of money for lunch. After all, this antique Chesapeake Bay town is famous for seafood, as well as sailing. Packs of Naval Academy cadets pass in front of me, enjoying crab cakes, oysters, and steamed clams. Their white hats look like dinner plates worn at a rakish angle.
So I slip my bank card into an automatic teller on West Street (laid out in 1696). Instantly, my request for $20 is beamed to Baltimore, where a bank computer realizes I'm an outsider. It throws my query to Dayton, Ohio. A computer ''switch'' in Dayton checks with my Washington-area bank, then tells Baltimore it's all right to give me money.
In 10 seconds, thanks to an electronic banking network, I have cash for a crab sandwich - and a computer in Dayton knows I have skipped out of the office on a sunny, early spring afternoon.
Today, magic webs of computers are rapidly easing many of life's little tasks: getting cash, shopping, sending messages. But at the same time, these webs are hauling in vast amounts of personal data on Americans.
We must keep a careful eye on the rise of automatic banking, electronic mail, and other systems, say experts, if our privacy is to remain protected.
''As a byproduct of the evolution of technology, we are developing a network of surveillance capability,'' says Arthur Bushkin, who was in charge of President Carter's privacy initiatives, ''although it's not out of any malicious intent.''
The institutions that run computerized transaction networks all pledge to fiercely guard their customers' data. Yet gray areas in the law, say congressional aides and communications lawyers, may make these actions legal.
* Your boss, spouse, or a credit agency could track your movements with the use of electronic banking records. No federal law bars banks from divulging this information to third parties.
* If you use electronic mail, law-enforcement officers might be able to read your messages without a warrant. Search warrants are needed to open letters carried by the United States Postal Service.
* Subscribers to two-way cable television may find that opinions they register are sold to, say, political parties, with their names attached. Currently, the only laws protecting two-way cable data are state statutes in Illinois, Wisconsin, California, and Connecticut.
Back at the dawn of the information age, when computers took up the floor space of a hockey rink, civil libertarians feared the coming of the Big Box - a giant computer compiling data on everyone in the US.
Instead, during the last 20 years little computers have learned to chatter back and forth, over communications links of unbelievable sophistication.
This gift of speech has made possible computer networks that today handle such tasks as reserving plane seats and approving checks. Decentralized, fast, hungry for data, these webs are far more than mere automated clerks, say those who follow privacy issues.
''More information is being maintained on individuals. It's being more centralized. It is more accessible and available,'' says Ron Plesser, a Washington, D.C., lawyer who was counsel to the 1977 federal privacy commission.
Today, the computers that know the most about us are probably those that handle financial tasks: electronic tellers, credit-card checking machines, and check authorizers. Besides knowledge of how much money we have in the bank, these systems know where we are depositing our paycheck, or paying $150 for clothes - at the very moment we're conducting the transaction.
And money computers will be even more knowledgeable in the years ahead, as networks grow and combine to provide more services. Soon, for instance, American Express cardholders will be able to charge calls on specially equipped AT&T phones; eventually ''debit'' cards are expected to link banks and retailers by automatically siphoning cash from our accounts as we make purchases.
''The computer can develop a data base on your preferences: He likes to shop at this store, etc.,'' says Art Bushkin, now a telecommunications consultant. ''It has time data. You can program it to behave preemptively: 'The next time Bushkin appears within the computer's scope, print out a message for the FBI (Federal Bureau of Investigation).' ''
Bank officials react indignantly when asked whether they might show this data to outsiders. Most financial institutions have explicit policies on protecting the privacy of their depositors.
But it is only the institutions' good will that guards these secrets, say privacy experts. The laws protecting financial records are very limited, they claim. If the federal government asks to see your bank files, the 1978 Right to Financial Privacy Act requires that you be notified. If a private party asks for them, it's perfectly legal for the bank to hand over the data without saying a word.
And if you think such things never happen, remember that Bob Woodward and Carl Bernstein, in pursuit of the Watergate story for the Washington Post, found California lawyer Donald Segretti's credit card records to be a rich source of information.
A Congressional Office of Technology Assessment study concludes that the need ''for more comprehensive electronic funds transfer privacy protection . . . are still largely unmet.''
If anything, there may be even less legal protection for message transmission systems such as electronic mail.
The electronic-mail business, long more promise than performance, is just now shifting into second gear. Private firms did about $40 million worth of business last year, and in September MCI Communications launched its ambitious MCI Mail service.
Yet these ethereal messages, which flit from computer screen to computer screen, are more vulnerable than old-fashioned letters in several respects.
For one thing, some clever users of home computers have managed to break into the networks. Last summer, a gang of Milwaukee teens repeatedly romped through GTE Corporation's Telenet system. No law explicitly makes this illegal. ''It's a very large gray area,'' says Walter Ulrich, a computer consultant and head of the Electronic Mail Association's privacy committee.
For another thing, both law officers and private third parties might be able to read your messages without your knowledge. MCI, GTE, and other electronic-mail companies all say they will staunchly defend their subscribers' privacy. No law, however, prevents them from voluntarily surrendering your mail.
''Chilling, isn't it?'' says Mr. Ulrich.
But it is still another type of computerized network that may have the greatest potential for invading our privacy: two-way cable TV.
Such systems promise to bring a world of services into our family rooms, via color TV. Futurists have long predicted that we will eventually be able to bank, shop, and express our opinion over interactive cable channels.
If so, we will be entrusting cable companies with huge chunks of data about ourselves: buying and viewing habits, perhaps even political and social opinions.
''This sensitive personal information is a valuable commodity which cable companies can sell to . . . interested buyers in order to finance their corporate growth,'' charges John Shattuck, national legal director of the American Civil Liberties Union.
No federal statute covers the issue. Four states, however, have passed laws prohibiting cable firms from disseminating individualized data. Two more - New York and Maryland - are considering similar laws.
The industry is sensitive to the problem. Warner-Amex Cable, which operates the QUBE interactive system in seven cities, subscribes to a privacy code that was the model for several of the state statutes.
Of course, all these systems - two-way cable, electronic mail, and electronic banking - promise great benefits. Privacy experts say they simply want to see laws prohibiting misuse of the networks.
And ''we should leave things flexible enough for the people who will want to continue the old ways,'' such as paying cash for gas, adds Robert Smith, editor of Privacy Journal.
Washington seems only mildly interested in the impact of computer systems on privacy. The House judiciary subcommittee on civil liberties, headed by Rep. Robert Kastenmeier (D) of Wisconsin is holding a series of hearings on the issue. The Commerce Department's National Telecommunications and Information Administration no longer works extensively on privacy.
''Do we as a society accept this evolution (of technology) and its implications passively?'' asks communications consultant Bushkin. ''Or do we discuss it and decide whether we like the way it is?''