QUICK STUDIES; BEFORE CLASSES BEGIN, YOUNG SCHOLARS GET THEIR ACTS TOGETHER.

Byline: Barbara De Witt Daily News Fashion Editor

Picture it. The year is 1965, and Mom has taken you shopping for your annual back-to-school wardrobe. It's no easy task, what with all those strict dress-code rules issued by the Los Angeles Unifed School District.

You know, skirts that had to be long enough to brush the floor when a girl got down on her knees (a typical test routinely conducted by surly vice principals). And everybody who was anybody had to have pricey dyed-to-match skirts and sweaters ... and a purse to match every outfit.

And guys? Let's put it this way: They were wearing the corporate version of casual Friday, long before IBM and Boeing discovered it.

Sneakers? They were reserved for P.E. class only.

Thankfully, school dress codes are more relaxed now. Class acts are also more unisex than in recent years, making shopping a no-brainer.

Just leave all the heavy metal at home so you can pass through the metal detector at the school entrance - and make sure your pants stay up without a belt.

Last year, the big trend was khaki, and while it's still in, denim is the fabric of choice for fall '98. ``It's always been popular, but it's experiencing a major resurgence ... and being reinterpreted in endless styles and finishes,'' says OshKosh spokeswoman Barbara Widder-Lowry. Like other retail experts, she reports over-dyed indigo blue as the denim of choice this fall.

Sears fashion director Fran Yoshioka says you'll see the new denim looking best in jeans that ride lower and flare wider - as wide as 30 inches in circumference.

``Self-expression is the key,'' explains Yoshioka, adding that children tend to dress themselves with reference points from their lives, including pop-culture icons and favorite pastimes such as skateboarding. So that's why you'll see more athletic looks, such as hooded tops, snap pants and outer seam striping on boy and girl members of the in-crowd. Honest, it's true. According to the Teen Caravan Survey for T.J. Maxx stores, 87 percent of girls age 12 to 17, preferred pants to skirts.

Sweaters are the big news on campus, report fashion experts from numerous retail stores, including J.C. Penney, which reports cardigans and matching shells are its current best sellers for girls.

Besides that classic twinset, look for traditional argyle designs (especially pullover vests), V-neck pullovers, knit tank tops and cable-knit cardigans topped with fake fur collars. A survey of local malls showed them with horizontal stripes, fuzzy ``eyelash'' yarns, graduated color yarns and embroidered and beaded floral designs circa 1950.

Guys also are wearing sweaters, including short-sleeved knit shirt-jacs, athletic striped pullovers and baggy turtlenecks that have a relaxed, slapdash 'tude.

Juniors, that fickle category of young female teens, are reportedly the hardest to please. According to the American Express Retail Index on back-to-school shopping, the average American family will spend $408 per teen ($300 on younger children), an amount that is ballooning because this age group is ultra label-conscious and wants something new every week.

When a teen-age girl says ``new,'' she may mean alternative fashions such as gothic-inspired ``Buffy the Vampire Slayer'' tops (available at Warner Bros. stores), jeans by designers Lucky or Angel (try major department stores), and slinky skirts and clingy tops sporting labels such as Porn Star, Girl Star and 26 red. If she's going to dress up, she'll probably shop for something with lace or feather trim, and the labels to look for are X0X0, Rampage and Mica, all of which can be found in the junior department of most department stores and teen boutiques. An old brand parents may remember is Esprit, which has bounced back into style, offering a variety of wrap-front and clingy dresses to wear when one's jeans are in the laundry.

Name recognition

But most teens - at least 58 percent - according to that same American Express report, prefer high-profile names advertised in fashion magazines. The nation's faves among boys and girls, reports American Express, are (in order of popularity) Tommy Hilfiger (the Izod of the '80s), Levi's, the Gap, Polo by Ralph Lauren and Calvin Klein.

Uniforms have become a popular choice at both public and private schools, and shopping for those kids has never been easier. In previous years, parents had to order uniforms from a catalog, but now they're available at most stores, including Wal-Mart, Kmart, Mervyn's, Sears, Macy's and Nordstrom.

The basics are tan or navy, with skirts, pants, long shorts and jumpers worn with white blouses or cotton knit polo shirts.

Shoes are the same, whether the child is wearing a uniform or not. The operative word is chunky, in oxfords and loafers for both boys and girls. But the sneaker, with retro detailing (such as stripes), is making a comeback.

Accessories are important, but thankfully (for the budget-conscious) not as plentiful as last fall. Girls are wearing patterned socks and tights, and hair clips with tiny crystals or butterflies, and everybody's strapping on sports watches with all the bells and whistles.

Backpacks continue to be the book bag of choice, but novelty totes such as Hello Kitty's hatbox design are newer. And instead of brown bags, the fresh take on lunchboxes is a zippered soft vinyl insulated box, hopefully in bright colors with a cartoon character on the front, to hold bottled water, juice boxes and turkey wraps or pita pocket sandwiches.

Personal space

That school wardrobe budget also needs to stretch to the locker. Now a personal space instead of merely a place to stash books between classes, there are entire aisles at mass merchandising stores dedicated to locker accessories. Among the hot tickets are shelves to fit inside the locker, magnetic mirrors, magnets for messages, magnetic bulletin boards and removable paper to cover the utilitarian beige or gray walls.

At this point, parents may be thinking how they were thrilled to get a new notebook and a box of crayons, but don't go there. Remember how you hated it when your parents told you about the five or 10 miles they walked to school through sleet and snow and how they had to write in pencil because Bic and Pentel gizmos hadn't been invented yet?

DO YOUR HOMEWORK

According to the American Express Retail Index on back-to-school shopping, families will spend about $300 per child on back-to-school wardrobes ($408 on teens), so spend wisely with fashion savvy. Here's the semester's mostly unisex must-have list to get you started:

Dark blue denim

Flared pants

Athletic stripes

Cargo pockets

Retro sneakers

Knit vests over white shirts

Chunky shoes

Hooded sweat shirts

Fake fur-trimmed cardigans (girls only)

Plaid capris (girls only)

White cotton dress shirts

- Barbara De Witt

CAPTION(S):

7 Photos, Box

Photo: (1--Cover--Color) On the cover: Classroom faves for fall include striped cotton T's by TKS Basics, $5.99, worn with Lee carpenter jeans, left, and TKS Basics khaki cargo pants, $12.99; all from Sears.

(2--Color) Ralph Lauren Polo sweater, $78, from Bloomingdale's.

(3--Color) Stripes are a hot ticket for back-to-school, especially on jeans like these by Retro Riders.

(4--Color) He's stylin' in jeans with a mega-wide leg, $24.99, topped with a cotton knit shirt, $17.99, available at Target stores. Note that retro sneakers are a fashion must-have for guys and girls.

(5--Color) For that uniform look, try Dickie's new collection available at Kmart, Wal-Mart and J.C. Penney stores.

(6--Color) Chunky clunkers are cool for school; by Airwalk.

(7) To accessorize your back-to-school wardrobe, add textured tights and socks by L'eggs, available at supermarkets.

Box: DO YOUR HOMEWORK (See Text)