The volunteer fire department of Deep River, Conn., had problems with radio communications jamming last year - partly because of a grocery store cash register and a church thermostat.
Both occasionally gave off radio-frequency waves that produced enough static to thwart communications.
Deep River's trouble points up a recurring problem for a world turning more to electronics: electromagnetic interference (EMI), a bristly name for errant waves that can foul up everything from television pictures to, perhaps, an aircraft's flight path.
You are already aware of most of the irksome effects of radio-frequency interference. It usually shows up as ''fuzz'' on your TV screen caused by anything from a hair dryer to a CB radio or a neighbor's garage door opener.
But as electronic devices proliferate, particularly computers, so does the number of potential sources of these ubiquitous but unseen emissions.
Result: The need to squelch static is capturing renewed attention from electronics manufacturers as well as from the Federal Communications Commission (FCC), which sets radiation emission standards on many devices.
The problem hasn't shown up in higher numbers yet. Last year the FCC received 65,000 interference complaints. The numbers have been declining since a peak of 130,000 in 1976, the height of the CB radio boom (CBs are a chief source of EMI).
Yet new concern about ''signal pollution'' surrounds the spread of computers and other electronic equipment. Computers generate radio-frequency waves as they do their work. Data are processed by a series of ''on'' or ''off'' electrical pulses. Each pulse produces a rise or fall in voltage level, which generates the waves.
Normally the equipment should not make enough waves to cause havoc - and usually it doesn't. The FCC limits emission levels of computers, microwave ovens , video games, and other devices. It backs up its limits with fines of up $10, 000 to manufacturers found in violation, and sometimes retailers who sell ''unshielded'' equipment - that which doesn't carry the coatings or filtering devices that prevent leaks.
Those that do slip through interfere with TV and radio reception in the home. In the office, the damage can be worse. Leaks from radio pagers, walkie-talkies, and electronic equipment have been known to wipe out entire computer data banks, or, on a lesser scale, to cause annoying computer errors. Serious problems arise in hospitals, too. Interference there has hampered medical machinery. ''It is in these environments that more attention has to be paid,'' says Glen Dash of Dash, Straus & Goodhue Inc., a Massachusetts consulting firm.
Perhaps the biggest concern, however, is over the ways electronic devices may affect aircraft. Many electronic gadgets are banned from use on planes, except for small items such as shavers and tape recorders. Others gadgets are allowed, if the airline has determined they won't foul up electronic control and navigation systems.
Enter battery-powered, briefcase-size computers and video games. Air carriers are eager to let passengers work (or play) while on board. But will Pac-Man zap the aircraft's compass needle? Most engineers doubt it. No serious accidents have been recorded as a result of radio-frequency interference so far. But the threat is real enough that a special investigative committee is probing the matter. The group, made up of representatives of government, airlines, and airline-related industries, met for the first time last month. There have been instances of leaks from video game arcades at airports garbling pilot-control tower communications. At least one carrier, Eastern, bans the use of computers on its planes, although it allows calculators.
In addition to the concerns about electronic toys and computers, leaks from cable TV systems are drawing a watchful eye from the Federal Aviation Administration (FAA). Again, no planes have been endangered by faulty cable installations or old lines. But the stray signals have caused pilots to miss instructions from ground controllers. New cable systems, though, are better insulated and should eliminate most problems, say FAA engineers. The upshot of all this is that signal pollution is far from a crisis. But it will demand increasing vigilance from the FCC and manufacturers, as potential sources proliferate - cordless phones, new FM radio stations, and computer chips in everything from ovens to coffeemakers.
''I can see someday when one person's cordless phone will make someone else's dishwasher go crazy,'' says Joseph Casey, chief of the FCC's inspection and investigations branch. ''They are examples of two devices that weren't even in the home five years ago.''