We all know that the problems of the working mother are her own fault, that if she were just efficient enough there'd be plenty of time for children, husband, job and Aerobics II. Guilt would be a thing of the past and exhaustion unheard of.

The trick is how to be efficient. There are lots of formulas handed down by our mothers and grandmothers. Things like, "A place for everything and everything in its place," "A stitch in time saves nine," "Do it before it needs doing" and "There's nothing that a little elbow grease won't set straight." None of these is particularly helpful.

The key to efficiency -- I've decided after reading a lot of articles on the subject -- is this: Do things once and never again. Repetition is the single most significant cause of inefficiency, just as inefficiency is the single most significant cause of wasted energy and time.

If it's worth doing at all, it's worth doing only once. That is the principle. Here are some ideas for applying it:

*Birthday Presents: Birthday parties are inevitable and presents unavoidable. Instead of dashing out every time one of your kids comes running up to you announcing there's a birthday party in an hour and they don't have a present, plan to make one trip to buy all the birthday presents for the next year, or the next decade if you really want to be efficient.

Make a list of all your children's friends and buy that many unisex presents (flashlights, records, books, gift certificates, yo-yos, etc.), plus two extra ones in case your children should make any new friends. Bring the gifts home and have your children wrap them in the unisex paper (purple) and ribbon (green) that you bought in lifetime quantities and store them away in the cupboard with tags filled out, signed and affixed.

*Halloween Candy: Halloween may catch you in an all-day conference on nuclear waste with no time to rush out to buy candy. Not to worry. Next to the cupboard with the birthday presents is a shelf on which you have a large coffee can filled with nickels, which you just bring out and dispense with a smile to the trick-or-treaters. No one ever got cavities from a nickel. You can be smug on two counts.

*Laundry: If laundry takes up most of your free time -- time you could be using to see "Gone With the Wind" again -- that's because you do the laundry too often, probably even once a week!

Here's the solution: You need two enormous cupboards with lots of deep shelves. Label the first one "Dirty Clothes." All the family members bring their soiled garments to the cupboard once a week and sort them onto the shelves, marked "hot, white," "cool, dark," etc.

Once a year everyone pitches in and, using your five sets of washers and dryers, washes the whole shebang in one day. The other cupboard is labeled "Clean Clothes" and holds prepackaged bundles you organized last time you did the laundry (and added to with shopping expeditions over the past year). Each bundle is organized by name, season and occasion. "Susie, summer, casual" would contain, for example, cut-offs and T-shirt. "Joe, year-round, formal casual" might contain slacks, shirt with matching socks and belt. Also included would be underwear and accessories such as ribbons, handkerchiefs, caps and sunglasses.

It takes a certain amount of preplanning and, yes, money to pull this one off.

*Dishes: First of all, get your dishes out of cupboards (you're going to need them for clothes, anyway) and into seven dishwashers arranged in rows across your kitchen (you can use the tops of them for specialized workplaces: breadmaking, sewing, papier-ma che', vegetable cutting, coupon sorting . . .). Label one "glasses," one "plates," etc., and take what you need from the bottom shelves so you don't end up having dirty dishes dripping on the clean ones you haven't used yet.

At the end of the week, barring a power failure, turn them all on and voila -- clean dishes for another week.

*Beds: You may have noticed that in the really expensive restaurants they have tablecloth piled on tablecloth. When a new customer comes in, the waiter simply removes the top tablecloth and the table is fresh again. This principle can easily be adapted to beds. When you make the bed, instead of putting on just one sheet, you put on 52 bottom sheets, 52 top sheets and 52 pillow cases. Every week you simply remove the outermost one until you come to the end. Then you take all that soiled linen -- stored in yet another cupboard -- and wash it in those (remember?) five washers and dryers.

*School Lunches: Catching on? There are 180 school days a year; for two kids, that means 360 lunches. Why do the same thing over and over again every day?

Plan a big shopping trip and buy 360 slices of bologna, 360 slices of cheese, 360 apples, 360 ounces each of peanut butter and jelly, 720 slices of bread and 720 cookies. In one afternoon you can make, bag, label and store in your new freezers all the lunches your kids will eat that year. On the shelf next to the can of nickels goes a can of dimes for milk money.

The above principle of one-time preparation and freezing can, of course, be applied to breakfasts, snacks, dinners, gourmet entre'es and "spur-of-the-moment" picnics.

*Warnings, Admonitions and Advice: On a day when you're in particularly good voice, gather your children together and deliver all the messages at once. "Wear your boots, wear your boots, wear your boots, don't go past Packard Road, don't go past Packard Road, don't go past Packard Road, get to bed, get to bed, get to bed, get to bed, get to bed . . ."

*Quality Time: Nothing matters more than the quality of time you spend with your children. This is not the time to take them to the grocery store, or buy them shoes, or sit with them and go over and over and over their math until they get it straight. Those are quantity times, and vastly inferior.

Quality times are when everyone has fun. The way to get these efficiently organized is to go to a movie with your kids at 10 o'clock some Saturday morning and if your children like the film, stay for the 12, 2, 4 and 6 o'clock showings. Five movies, five quality times -- enough for five weeks, at least.

There are, of course, some limits to the do-it-once principle, such as being able to eat enough at one time to get through the month, or sleep enough or exercise enough.

And these things, it must be admitted, will never lend themselves to a once-a-month schedule: hot baths, cuddling a baby, eating chocolate, making love, strolling under bright blue skies.

These things you must -- with shameless inefficiency -- repeat over and over again.