With hisses, pops and crackles, frequency interference is the paper cut of the telecommunications spectrum--painful and annoying.

But as the Federal Communications Commission continues skipping down the deregulatory path, more and more telecommunications services are competing for niches in a dwindling spectrum. Cordless phones, citizen band radios, personal computers and cable TV are all part of a frequency mix that occasionally gets mixed up. The resulting snow and static increasingly is becoming an FCC concern.

"There are more and more things susceptible to an interference problem," says Joe Casey, chief of the FCC's Inspections and Investigations Branch. "When there are interference problems, we'll go out and investigate.

"We get between 60,000 and 80,000 interference complaints a year to our field offices and that's held steady over time. That's partly because the public is getting used to non-perfect reception. Interference is a fact of life."

It can also be manifested in mysterious ways. "When thermostats get dirty," Casey explained, "they can start to spark and that can cause interference with TV and radio reception. Sometimes when we get interference complaints we advise people to vacuum the dust out of their thermostat.

"We've also had cases of fish tank motors disrupting reception and jamming the conversations on cordless phones."

Working with the FCC regional offices, Casey's group reports that CB radio generates the lion's share of spectrum fuzz. CBs have been blamed for such things as lighting up touch-sensitive lamps, setting off smoke detectors and breaking into a synagogue's public-address system during a Bar Mitzvah service.

NASA currently has a satellite in space that is geared to track "crash beacon" emissions from wayward aircraft. The program is administered internationally and the FCC is responsible for much of the U.S. portion.

The FCC's laboratories in Laurel are responsible for sampling and testing new electronics products that might be "dirty" and poison the frequency spectrum with interference. An administrative and engineering staff of 14 people checks out the latest in personal computers, television sets, CB radios and cordless phones to see whether they fall within acceptable noise levels.

Will A. McGibbon of the laboratory staff says members test "300 to 350 devices a year." However, he makes the crucial point that the FCC tests only how much interference a device may cause, not how susceptible a device may be to interference. That, he says, may prove to be the most important factor as telecommunications deregulation continues. "The more devices you have out there that have the capability of interfering," says McGibbon, "the more likely it is that there will be interference."

However, both he and Casey say that the way the FCC put stringent requirements on personal computers helped prevent a Babel of interference. "Even though computers have exploded on the marketplace," says Casey, "there hasn't been that much interference."

So, despite the fact that this commission is philosophically committed to structural deregulation of the telecommunications market, observers both inside and outside the agency emphasize that it isn't about to interfere with the technical standards that keep the spectrum from collapsing into chaos.