If wearing your heart on your sleeve is old hat, why not put the quintessential valentine symbol on your walls? That's what interior designer Susanne Shaw did, papering a guest room with red wallpaper adorned with tiny white hearts.

Heart-pattened wallpaper is an idea whose time has clearly come, says Maurice Murray, publisher of the Wall Paper, the billion-dollar-a-year industry's bible. Not long ago, says Murray, butterflies were the rage. Now, there's a penchant for small-scaled repetitive patterns, typical of wallpaper with hearts.

Admittedly, you can't use hearts just any place. "It's a gentle sort of design, appropriate for a limited number of very special places," says Harry Hinson of Hinson & Co. "I don't think you'd want them in your living room."

D. Porthault's "Hearts" and "Double Hearts" are an excellent case in point. For years, the fancy French linen firm has carried bed sheets covered with pink, blue, green or yellow hearts. Recently, Porthault started manufacturing matching wallpapers. According to the company's North American representative, Los Angeles designer Gerald Miller, the bathroom walls of Hollywood luminary Ann-Margret are adorned with Porthault's pretty pink hearts, Mrs. Walter Matthau has them in her bedroom and even Gloria Vanderbilt (who, having a wallpaper line of her own, declined to comment on a rival) has ordered some.

In addition to Porthault, carried locally at Jane Wilner, Ltd. and Dolly Kay Originals, here are more wallpapers that have a heart:

*Interials, Inc. makes "My Heart Belongs to Daddy," multi-colored outlines of hearts within hearts (primary colors on white or yellow and various shades of orchid on pink).

*Country Gear's C.I.T.Y. collection features stenciled "Hearts," a border by Ramond Gear, a former Marimekko designer. It is available through Cherisables, on Thomas Jefferson Street, and Country Sampler, in the Foundry Building.

*International Printworks by Waverly has "Hearts," which comes in red, pink, lavender or yellow on a white background; "Scattered Hearts," with slightly larger hearts in crayon colors; and "Heart Shower," tiny hearts in pastel colors. Looking for a really small pattern? Katja and Marimekko have the most diminutive and contemporary-looking hearts in the business -- less than a quarter of an inch high.

*Gift-wrap may seem an unlikely source of heart wallpaper. But at Affairs of the Heart, a Georgetown Park store specializing in merchandise garnished with hearts (and papered in Marimekko's two-toned red and green hearts), owner Phlyyis Spaisman recenlty discovered that Georgetown University freshman were using her $2.50-a-roll wrapping paper to paper their barren dorms.

*The dernier cri in heart papers, however, are patterns with a past. The Hinson Collections based its brand new "Country Heart Print," "Country Heart Stripe" and "Country Heart Flower" on a Pennsylvania German folk design in the Metropolitan Museum of Art's New American Wing. The coordinating wallpapers, which come in a variety of colors, are available locally at Designare Ltd., on Connecticut Avenue; Jean Becker, Alexandria; Butler Flynn Paint Co., Chevy Chase, and Snyder & Co. in Arlington. CAPTION: Picture 1, "LES COEURS," Hinson & Co., available through interior designers ($34.50); Picture 2, "SCATTERED HEARTS," at Georgetown Printworks and Union Wallpaper ($22.95); Picture 3, Waverly's "HEARTS," at Georgetown Printworks and Union Wallpaper ($18.95); Picture 4, "MY HEART BELONGS TO DADDY," Interials, Inc., through Interior Designers ($39); Picture 5, Porthault "HEARTS," at Jane Wilner, Ltd., and Dolly Kay Design, Ltd. ($30); Picture 6, Bedroom by Susanne Shaw, at Pardoe & Graham's Villas at Potomac Cliffs, whispers romance with rd-and-white heart wallpaper, Lina Brown Number 9255 ($9.95 a roll), at Union Wallpaper & Paint, 4860 Massachusetts Ave. NW. By GLEN LEACH