Like all mystery men, Valerian Stux Rybar claims he is not mysterious at all.

"Oh, everyone knows all about me," he says. "They're always writing me up."

Maybe so. Certainly the Nicholas du Ponts Palm Beach some years ago - setting off a national rage for bamboo furniture. Jerry Ohrbach knows him, because he did Ohrbach's Beverly Hills home. And Christina Onassis and the Guy de Rothschilds in Paris and Pierre Schlumberger and Herbert Von Karajan and Prentis Cobb Hale and Wiley Buchanan and Henry Ford's uncle, Herbert Kanzler, and the Antenor Patinos of Portugal.

The Patinos know him very well indeed, because he spent a year and a half working on the ball they gave for 1,000 intimate friends a few years ago - a ball described as "the most important since World War II and perhaps the luxury party of the century." One feature was a gigantic coral chandelier: artificial coral to be sure, but coral nevertheless. It's the concept that counts.

In his own New York apartment, Rybar has textured stainless-steel floors ("you never have to wax them, they're skidproof. And so durable . . ."), velvet folding chairs and a steel banquette covered in handpainted ponyskin that goes up and down electrically and can be a massage table, an ironing board or a place for packing.

Also: a mink-tail rug, curving walls in red linen velvet, chrome moldings and baseboards, red-brown-black marblized embroidery on satin-pillow steel ottomans, vertical steel blinds, marble-topped steel tables (touched up with bowls of silver baubles and gilded lobsters), tortoise-shell-and-nickel bathroom fixtures, chocolate carpeting in the bathroom and mirrors on the closets - that hold, in fanatically neat array, his 150 shirts, his 40 seasonal suits (all beige), his 40 pairs of shoes, his 100 belts and a whole doorful of his ties.

He was born in Sarajevo; and his Hungarian father, a banker, had a jacket with a bullet hole in it (he having been a guest at the reception for Archduke Franz Ferdinand that day in 1914). He speaks five languages, all with an accent ("English is my first language, because of my English nanny"). For seven years he was married to brewing heiress Aileen Guinness. He travels 200,000 miles a year, as much as an airline pilot, and his specially-made Gucci luggage includes:

A shoulder bag containing two stud boxes, a watch case, a case for currency from 12 countries, a leather ticket-and-card billfold, a leather envelope for shopping records, an eyeglass case, a wallet, his current book, six address books organized by countries.

An attache case containing a business notebook, two checkbooks, an appointment calendar, a dictaphone, rules in inches and meters.

A portfolio for presentation sketches by his staff.

A large rigid case for samples and files.

Two soft suitcases for clothes.

His interest in order goes far beyond mere neatness.

Fascinated with bedroom and bathroom design, he pioneered the bath-dressing room; the all-mirror room; leather walls; furniture of tortoise shell, horn, onyx, mother of pearl and lapis.

Fascinated with clothes, and a regular on 10-best-dressed lists, he designed, had made and launched: the wearing of slim boots with suits; shirts and slacks of batik, paisleys, suedes, embroidery; velvet facings; the all-white, all-velvet, all-silk dinner jacket; embroidered vests; navy-blue men's shoes; the all-tweed suit.

Called in to redesign the interior of the Ohrbach mansion, formerly Robert Taylor's place, Rybar found: a vast entrance hall, formal drawing room, casual living room, breakfast room, elaborate kitchen, huge guest suite, working fireplaces in most rooms, a movie theater for 25, a tennis court, wine cellar bomb shelter, free-form pool, 12-car garage and innumerable other features.

Some of the things he did: imported stone for the living-room floor from Portugal; installed Versailles-like parquet floors in the drawing room; had rugs woven to order; designed everything from bookbindings to billiard tables and had them made in places all over the world; rebuilt the His master bathroom as an octagon in gray marble and mahogany with barber chair, sauna, shower and toilet in separate chambers; rebuilt the Hers master bathroom as an oval with special hairdressing chamber and arranged for the wall fabrics to be changed seasonally along with the linens.

He spent nearly three years on the job. The hardware for the fittings alone cost $120,000.

He has decorated the Tropicana in Las Vegas Britannia Beach restaurant complex in Nassau, the Royal Hibernian in Dublin, the Valentino boutique in Paris, El Morocco nightclub, and supervised the entire design concept of the $30 million tres Vidas resort at Acapulco, not to mention Atlantic City's elaborate Haddon Hall casino-hotel layout.

his one-shot projects range from Susan Englehardt's $110,000 coming-out party to several editions of the April in Paris Ball here, the International Ball in Washington, the Fete Champetre of the Marquis de Cuevas at Blarritz, a big Tiffany exhibit, Dior's Christmas decor, Henkel's centennial show in Dusseldorf and a charity gala at Versailles.

If Valerian Rybar did not exist, he could never have been invented.

"I was going to be a lawyer," he said over an elegant lunch of cold bass and marinated artichoke. "I went to a fancy school in Vienna - my mother was Viennese - and spent two years in law school in Sweden but was rescued from tht career by World War II, which I spent serving in Dubrovnik. Can you imagine me as a Serbian lawyer?"

Shortly after his arrival in New York on a Swedish passport, he designed a mask for a friend going to a bal de tete . Its heady fantasy attracted the attention of Elizabeth Arden, who hired him as a package designer, then quickly promoted him to designing her shops. Three years later he started off on his own.

Today he divides his time between New York and Paris, keeps two apartments and two wardrobes, takes on two or three office projects, a couple of hotels and three or four houses a year. Travel is his way of life. He does not eat or drink on a plane but uses the time for "my best thinking." He deals with jet lag by plunging straight into the new time, taking sleeping pills if necessary. He has been almost everywhere you can think of.

A former assistant, Ron Jehu, described his five years with Rybar before dropping out to become an artists' agent and gallery owner in San Francisco:

"He'd specify the details and I'd execute them. On a big job there could be 100 big sheets of drawings: moldings, cabinets, windows, electrical details. he was even responsible for the placement of walls, reshaping rooms. He'd start from scratch, often. He used to lean to an 18th-century French influence, but a few years ago he went modern in a big way."

Jehu, a Pratt Institute graduate, brought to his work a solid knowledge of drafting, wiring, plumbing, furniture design and the technical aspects of color. he needed all his skills for his wide-ranging job.

"The rich were almost in awe of him, I think. He would always stage one big explosion and would walk off the job and everything. It kept 'em in line. Some people think his work is overdone, but he's never stereotyped. Velerian's spaces never look like anyone else's. But he doesn't repeat."

Lunching at the Hermitage, down the street from his offices, Rybar, 54, tanned and quietly elegant in brown suit and gray-brown tie, was mildly irritated at not being recognized.The owner was away, he was told; and after a polite, formal exchange with the maitred', he seemed content. During the interview, in a book-lined, brown-and-steel study, he excused himself gracefully at intervals to take urgent calls from Paris and Portugal, each in appropriate language.

Some Rybarisms:

"I find brown a very peaceful color. Some colors I never work in: lavender, purple, fuchsia. But color isn't the key to good design. The most important aspect is to be functional. It's perfectly possible to be functional yet luxurious."

"The emphasis on bathrooms is pleasure: Everybody's already, clean these days. I think a feeling of sybaritic well-being should be suggested by a decor in very subtle ways."

"I love to do parties if one comes along, but I'm afraid party time is over."

"I don't want people to ssay, 'This is a Valerian Rybar interior,' but "This interrior is so . . . right that it must have been done by Valerian."

"A designer's function is like a set designer in a theater. The personality of the owner is as important as the playwright's notes."

"Americans travel in the same blue business suit they'll wear at the conference. But that's changing."

"I can carry proportions and colors in my head. I can pick furniture in England for a house in Greece I've never seen. I think this is a Gemini thing. I'm a Gemini."

"Built-ins are the furniture of the future. Most furniture life chests of drawers will be obsolete soon. Lighting will become more important, too."

"I never did like the Swedish style so much. Not sensual enough. Decor should be fun."

"I suppose," Rybar mused once in all candor, "I'm the only international American designer since Lady Mendl." He wasn't boasting just making a statement. He smiled. Mysteriously.