SWIMSUIT STYLES DIVE BACK IN TIME : SUITING UP IN STYLE.

Byline: Barbara De Witt Daily News Fashion Editor

Bikinis are back. So are boy-legs, halters and Hawaiian prints.

Elena Hart, spokeswoman for the Fashion Association in New York, calls the season's swimsuit direction both glamorous and girlie. ``There's a vintage approach inspired by movie stars like Marilyn Monroe and those old cheesecake swimsuit calendars, and also a '60s mood reflecting the classic elegance of Halston gowns and the personal style of Audrey Hepburn,'' said Hart.

For the cheesecake style, you'll need a two-piece suit with boy-cut legs that look like short-shorts in polka dots or plaid, madras or seersucker. Since this suit is modest and comfy, it's great for volleyball and swimming laps, but you can quickly glam it up with a pair of high-heeled sandals that show your painted toenails, cat's-eye sunglasses, big hair and red lipstick.

The Audrey Hepburn style relies on evening-wear silhouettes with one-shoulder or cross-back designs that fit like a glove, thanks to lycra, supplex and microfiber techno-fabrics, Hart added. These suits are usually a solid color with Gucci-like details such as lingerie straps, illusion netting and sexy cutouts, but Halston's signature one-shoulder strap is the ultimate for evening dips.

You'll find the suit well-suited to basic black, but fashion experts such as Bill Bigler of Macy's West stores, predict this to be the year for color, whether it's tobacco brown or red.

But back to the beach, where you'll be spotting more bikinis than you've seen in years, according to Mitzi Birdsong, swimwear buyer for JC Penney stores. She says the popularity is based on a variety of retro options, from triangle tops to string models, which were last seen in the late '70s.

With all that skin showing, you'll need a cover-up, and Birdsong says the newest is the sarong, also called a pareo. ``Not only are they easy to put on, they hide the hips and fit a variety of figure types,'' she added.

Suiting up is one of life's biggest challenges. Somehow, that little bit of lycra has to make you look like the models in the magazines. You know, tall, thin and bronzed.

To help you get the swimsuit that suits you best, slather on the fake tanning cream the night before, then take this checklist with you:

1. Ignore the numbers. Most swimsuits are made a size larger than your street clothes.

2. Know your figure problems. If you've got thunder thighs, look for the new boy-legs instead of high-riding French-cut suits. If you've got a large bustline, be sure to get a suit with underwire support and wide straps. And if you're a tad flabby around the waistline, try a suit with built-in support to whittle your waist.

3. Look in the mirror. Take a good hard look at yourself from the front, the side and the rear. Then bend over, touch your toes and look again. If everything stayed smooth and didn't ride up, it's a keeper.

CAPTION(S):

6 Photos, Box

Photo: (1) Retro-inspired white two-piece with halter top and boy legs, accented with daisies by Guess? at Diane's swimsuit store at the Promenade in Woodland Hills, Fashion Square in Sherman Oaks and the Oaks in Thousand Oaks.

(2) For the summer of '97, cover-ups take a '40s stance with sarongs by Hunza.

(3) Anne Cole creates the illusion of a bikini with mesh insets that hide surgery scars.

(4) For the active, Citrus offers this two-piece suit trimmed in lime.

(5) Sporty touches - such as this drawstring waist - are new from Roxy for summer.

(6) High-cut legs on a classic maillot by Citrus.

Box: Suiting up in style (See text)