UNDER THE SUN : RETRO BIKINIS, TROPICAL COLORS, ONE-SHOULDER STYLES - THIS YEAR'S SUITS COVER EVERYTHING ...

Byline: Barbara De Witt

Bathing beauties are back. Fashion designers are in a glad-to-be-a-girl mood this spring.

We're talking about those girdle-like swimsuits with halter necklines and modest boy-legs, worn with platform sandals, that enhanced the pinup appeal of Betty Grable, Marilyn Monroe and Lana Turner.

``It's a vintage approach to what was once called `cheesecake,' with designer influence - think back to Halston,'' said Elena Hart, spokeswoman for the Fashion Association, a New York-based trade organization. Many of the same silhouettes - one-shouldered gowns, iridescent fabrics and criss-cross backs - that we saw at the Oscars have been incorporated into this season's swimsuits, Hart said, and she finds the result a welcome relief from the bare-all suits.

``Those French-cut legs showed too much cheek ... and as boomers are aging, they're rethinking what worked for their mothers in the '50s, namely the figure flattering boy-cut leg that covers the hip and top of the thigh,'' Hart said.

Linda Minjares, president of the swimsuit company Hot Water, said, ``Today's young women can't get enough vintage fashion, so we have re-created styles and patterns they love in an updated version for the '90s.''

Macy's fashion director Bill Bigler also has observed the demand. ``Prints and fabrics have come to closely reflect what is happening in the ready-to-wear markets at all levels ... so you'll see more color, stylized florals and Palm Beach prints,'' Bigler said. He said the focus on nostalgia has also gotten some hype from the bikini's 50th anniversary this year.

Retro shapes demand retro patterns, said Mitzi Birdsong, swimwear buyer for J.C. Penney stores. As a result, ``While solid hues remain a poolside fixture, prints abound. Look for stripes of all sizes, the retro punch of flower power and optical graphics designed to make your head spin.''

In this dial-a-decade mood, she added, you'll find suits made of textured fabrics such as crochet, ribbed knits, seersucker, pique and terry as well as shiny Lycra exercise-style fabric.

Watch some reruns of ``Gidget,'' ``Laugh-In'' and ``The Brady Bunch,'' rethink lime green one more time, and you're there.

Corbin Seitz, fashion consultant for Target stores, said ``pumped-up color'' such as cyber brights of orange, yellow, purple, turquoise and green are splashing swimsuits and accessories this season. The trend allows you to wear those bright-colored mules you can't wear to the office.

While designers such as Anne Klein are resurrecting the ultra-glam one-shouldered suit, several new swimsuit manufacturers are also wading into the nostalgia business. Take Bodacious, which is making suits for Marilyn Monroe wanna-bes; Isaac Mizrahi, with itsy-bitsy string bikinis in girlish gingham; Gideon Oberson with zip-front boy-leg maillots updated with vinyl accents; GirlStar, with flirty '60s styles; and Mossimo, the Los Angeles designer whose spring collection includes one-piece halter suits of the '40s and the triangle bikinis of the late '60s.

So, what's for you, ``Gidget'' or glam? With the latter, you can appear taller and thinner in high-heeled mules while showing off pink or green toenails. Either way, most of the latest styles will finally hide appendectomy scars.

Flatter - or flatten -

your figure

It's that time of year when you've got to bare your soul and all your figure flaws besides. In your search for the perfect swimsuit, be sure to check out these pool cues:

For women with large hips and thighs:

To minimize those thunder thighs, avoid tight belts and elastics that bind and create bulges.

Choose suits with full back coverage.

Opt for figure-flattering tunics and boy-cut legs.

Look for dark colors with design elements or bright accents at the top, or overall prints that keep the eye moving.

Choose an ``illusion'' suit with dark leg insets.

To conceal tummy bulge:

Camouflage the tummy with surplice wraps, contrast panels and mitered stripes.

Try suits with dark sides or vertical stripes, which visually pare physiques.

Slip on a soft, blouson style to shift emphasis from the waistline.

Look for suits with control panels.

To boost the bustline:

Look for suits with underwire bras and booster padding.

Add interest to the top (like ruffles) and minimize the bottom.

Shop for suits with soft, molded cups.

To minimize a large bustline:

Look for suits sized by a bra cup.

Consider underwires for support.

Try bandeau or halter tops in a dark color.

If you've had a mastectomy:

Try a high-necked sport tank or a retro halter style that has enough fabric to conceal a prosthesis.

Check out the styles designed specifically for breast cancer survivors with maximum chest and arm-hole coverage.

Opt for suits with ruffles at the bustline.

Source: J.C. Penney

Pool party trends '97

Tropical colors and prints

Retro styles, including halters and boy-legs

String bikinis

Textured fabrics

Activewear influence

Glam accessories (mules, sarongs, hats)

CAPTION(S):

7 Photos, 2 Boxes

Photo: (1--Cover--Color) On the cover: Charlotte Ross suits up in a '60s-inspired two piece design by Sassafras, $72, at Macy's. Makeup by Agostina/Celestine Agency; hair by Scott Lane Pettyjohn; styling by Barbara De Witt.

(2--Color) Charlotte Ross in a Halston-inspired suit by Anne Klein, $82, at Nordstrom and Macy's.

(3--Color) Ross, co-star of the new Fox sitcom ``Pauly,'' suns herself in a velvet daisy-print bikini, $69, with matching wrap skirt, $35, by Studio La Blanca. Those witty platform shoes are by Zodiac, $39; all from Macy's.

(4--Color) For that '40s glam look, Ross pairs a halter-necked two-piece suit by Bodacious, $82, at Neiman Marcus, with lace-up mules by Candie's, $65, from Macy's.

(5--Color) Ross sizzles in a silver lame bikini by Bodacious, $66, available at Neiman Marcus and Bloomingdale's.

(6--Color) Turning heads at the pool party is Ross in a classy red suit by Anne Klein, $88, at Robinsons-May.

(7--Color) For skating along the beach, Ross favors a sunsuit with ``boy-legs'' by Sunset Beach, $46, from Macy's.

Tina Gerson/Daily News

Box: (1) Pool party trends '97 (See Text)

(2) Flatter - or flatten - your figure (See Text)