There comes a time, somewhere toward the end of August, when a mother looks at her child and gasps in horror. Instead of the beautifully coiffed child that finished school last June, she sees a hairy little beast, a veritable "Cousin It" (if you remember the hair-covered creature on. "The Addams Family"). It's time for the annual back-to-school haircut.

It's also time to take a look at what sort of hair configuration you've been subjecting your child to. It's possible that he or she is sick of looking like Dorothy Hamill, Buster Brown, Heidi or the forever-young, still-popular "John-John" Kennedy look. Or it might be getting a little embarrassing to be seen on the playground with a cut looking suspiciously like the shape of your salad bowl or a hack job done with your $8.95 home clipper set.

It's always been a basic rite of passage for a daddy to take junior to his very own barbershop for his haircuts. Though most children think it's lots of fun to sit in the big high chairs with a lollipop plopped in their mouths, every barber has horror stories to tell of children's haircuts - of masses of chewing gum, Tootsie Rolls etc. hidden in the locks, or mothers who stand nervously by, begging not to cut too much of her precious one's curls.

"Mothers usually cut their child's hair until it gets too awful and then bring it to us for cleaning or mending," says Nancy Carrescia, manager of the Saka Fifth Avenue beauty salon. "Most children are very sure of what they want. The most important thing is what their peers say about their new cut. And it is often the case that once you start a new haircut on a little girl, all of her friends come in and ask for the same thing."

Frank Farmer has been specializing in children's haircutting for about 50 years and has been out at the Chevy Chase Woodies for 26 of them. He's working on the third generation of some families, and he says that haircuts haven't really changed much over the years.

"There really aren't any new hairdos," he says, "there are just new names for them." What he does is a basic English haircut for his young clients (up to 22 per day) and says that most mothers still prefer the hair of their child to be on the longish side. Saks Fifth Avenue also reports that the basic "choir boy" classic style seems to be the all-around favourite.

Though many hairdressers have cut hair of infants as young as seven months (who are held in their mother's laps during the cut), there is usually no need to take your child to a professional until around age 2 1/2 or 3. "But children don't like to be forced to have their hair cut," says Farmer. "You have to try and prepare the child for the experience so they know what to expect."

It's no use trying to corral your child into a stylist's chair and give instructions to lop off a few inches: Children, are too sensitive about their looks these days to stand for it. In fact, in New York, Kenneth, hair stylist for the glittery set, has opened two posh children's salons - one at Macy's and one at a swanky Madison Avenue children's boutique called Pumpkins and Monkeys. There, if you've got the time (an hour or so, plus the trip to New York) and the money ($12.50 for a regular wash-cut-dry) to treat your child to a little luxury, your junior fashion plate can even have a hot oil treatment or a party set. There's nothing quite as posh in Washington yet, although Saks Fifth Avenue will be opening up a special "Little Snippery" ("no parents allowed") that will also feature before and after photos of cuts.

Many parents take their children to their own barbers or hairdressers. That's fine if your stylist enjoys doing children. Most large beauty salons have someone who specializes in children, so ask when you call. There are also places, like The Hair Cuttery chain, which don't have a children's specialist per se, but whose regular cutters do a nice job on children very cheaply ($3 for cut only).

You can also consider improving your home cutting technique by learning some tricks of the trade. A good recent book called "How to Cut Children's Hair" is a good investment and has clear, easy directions and drawings. But remember, you'll need lots of practice, patience and a good sence of humor.

Children's hair is different to work with from grownups' - in fact, it's still really going through different stages until age 15. Boys' hair tends to be healthier - girls tend to have fine, limp hair as children.

Here are some pointers to keep in mind:

For a first-time haircut, make sure you tell your child what to expect and maybe bring along some of his or her favorite books or toys.

If your child cries during shampooing at home, there's no need to expose the whole salon to screaming by having the child's hair shampooed there. Wash the hair at home and make sure you've using a gentle shampoo.

Discuss beforehand what both of your ideas on how much hair is to be cut off to avoid an embarrassing scene.

Never give a child a permanent - the chemicals could retard the growth of young hair. For special occasions, try a pretty bow or combs instead of curls.

Don't always put your little girl's hair in a ponytail - even elastic coated bands can cause thinning out of the pulled-back hair if used too frequently.

Although blow-drying is okay, too much of it can cause dryness and make your hair strawlike, just as it can on your own hair. Besides, with a good cut, you shouldn't need to blow dry - just let it dry naturally. BACK-TO SCHOOL SPECIALS

THE PIERRS-MUCHEL SALON at Bloomingdale's White Flint will be offering a back-to-school special - for kids up to college age: $10 for a shampoo-cut-blow dry. For back-to-college, it's $15.

THE LITTLE SNIPPERY at Saks Fifth Avenue (5555 Wisconsin Ave., Chevy Chase) will offer free kids' haircuts on the lower level this Saturday, August 26, from 10 to noon. WHERE TO GO

Most department store salons and private beauty shops require appointments and weekends are the busiest times, so call well in advance. Ask if you are unfamiliar with the salon. Be prepared to spend $5 to $10. The walk-in places (like The Hair Cuttery) don't have appointments, so be prepared to wait on a weekend when they are quite busy. WHAT TO READ

How to Cut Children's Hair by Bob Bent. $5.95 in paperback (Simon & Schuster) at Saville Book Shop (3235 P St. N.W.) and Maryland Book Exchange (4500 College Ave., College Park), among others. FOR WOULD-BE BARBERS

Check your local beauty supply shop for cutting supplies and good prices on haircare products. Scott's Beauty and Barber Supply Co. (1915 Michigan Ave. NE) has four kinds of shears ($11.50 to $18) and special hair-cutting shears (like scissors) from 4 to 7 inches ($11.95 to $17.95).