A great deal of scientific research has been done in the past decade to try to explain the phenomenal increase in the number of working mothers. Some have laid this at the doorstep of divorce, others blame it on the economy and still others have attributed it to household boredom. The trend has been studied by government agencies, institutes of higher learning, children and husbands, not to mention in-laws. But all have overlooked the single most important factor, if not in sending mothers into the work force, at least in allowing them to stay there.

The telephone.

It would be impossible, I submit, for mothers to work outside the home if they did not have telephones. This may come as something of an annoying revelation to employers who have narrow notions about using the office phone for personal business, but in fact it has very little to do with personal business and everything to do with work. Without it, working mothers would be spending half their time enroute home.

Modern working mothers are learning or have learned the fine art of raising children by telephone. This might sound a trifle impersonal, but think of the alternative, which is to let them loose in the neighborhood to bring their troubles and ailments to the neighborhood mother who has chosen to stay at home.

I have a friend who hit the paid work force the year before her eldest child entered college, leaving an adolescent daughter to fend for herself in the afternoons. One day the daughter called her mother at work to report that she was sick. Her mother told her to take her temperature and then, instead of calling a doctor, her mother called me.

"Marcia's sick," she said, anxiety pulsating across the telephone lines. "And I can't decide whether to go home and take care of her or not. I feel guilty not being there. Here she is with a temperature of a 101 and I just don't know what to do."

"A hundred and two was always my cutoff," I answered. "Under that, I stay at work. Also, small cuts aren't eligible for on-site care, nor are mere sprains. Blood has to be gushing and the bone has to be broken."

"You're kidding," she said.

"No, I'm not. You've got to learn to set standards. You can't go running home every time one of your kids has a problem, otherwise you'll never get your work done. You've got to learn to use the phone. Tell Marcia to take a couple of aspirin and call you in an hour."

The telephone is particularly useful in disciplinary procedures in which you know that you will not be able to keep a straight face while grounding a child for some dreadful but nevertheless highly amusing caper. It's a lot easier to holler "and furthermore you're grounded for a week" into the mouthpiece of a telephone than into the cherubic face of a beloved child.

It is also much easier to stick to curfews when they are imposed over the telephone and you don't have to go one-on-one against the pleading eyes and beseeching voice of a child who is trying to tack yet one more unreasonable half-hour onto the time that he or she is loose in the land.

There are, however, disadvantages to raising children by telephone, not the least of which is that it is more difficult to tell when they are fibbing. Most mothers develop a fairly reliable set of fib antennae, which can detect the subtlest changes in the eyes, the tone of voice, the shifting of feet, the odd glance at the wall when they ought to be looking directly at you. Unusually rapid gesturing of the hands has also been known to signal trouble ahead, as have artificially relaxed postures on the sofa. None of these, however, can be spotted on the telephone. Because children quickly realize this, they lose some of the nervousness that usually accompanies fibs and that is, after all, the best giveaway.

Raising children by telephone is also difficult when one is dealing with a small child who is past the gurgling stage and not quite at the talking phase. This puts the working mother in the peculiar circumstance of sitting at her desk making baby noises into the telephone while her coworkers pretend nothing odd is going on.

This used to be the particular province of women, one of those embarrassing moments that would bring color to the faces of working mothers. Not too long ago, however, I realized that the phenomenon of raising children by phone has really taken hold. I heard the heartening sounds of a man doing it.

Without a trace of embarrassment, he was talking baby talk into the phone.