In two short years as a designer, Pat Henderson has sold her fashions in 19 of the United States and around the world. Among her patrons are actors, politicians, writers and diplomats. The wife of the late Egyptian president Anwar Sadat, columnist Earl Wilson and actress Sarah Vaughan are just a few of the celebrities who own Henderson originals. Elizabeth Taylor even ordered a lavender lame' coat custom-made to match her famous eyes.

Elizabeth Taylor has never worn the coat. It doesn't fit. That's because Pat Henderson, the self-proclaimed "Dior of Dog Fashion," made it for Taylor's pet Shih Tzu. With loving care, the former New York fashion model designs everything from evening wear to jogging suits to life jackets, all for four-legged clients. Henderson's company is called Silk-'N-Satin, although coats are also made of cashmere, tweed, fur, gold lame' and quilted down.

It all started in 1982, when Henderson, who says "all mothers sew," made green coats and shamrock hats for her poodles, Gigi and Yoda, and took them to New York's St. Patrick's Day parade. Spectators stopped her to ask where they could buy the outfits. The following month, for the Easter parade, Henderson dressed Gigi in white eyelet and pink satin, while Yoda sported a turquoise sailor suit with brass buttons. Delighted pet owners placed orders on the spot.

Henderson saw that there was a demand. Designing and sewing herself, with daughters Kathleen and Eileen handling administration and accounting, Silk-'N-Satin was born. Starting with a few orders from private clients in New York, word of mouth spread to department and specialty stores. Before long, Henderson was approached by Macy's in New York, Neiman-Marcus in Dallas and the famous Harrod's department store of London.

"The reaction was bigger than I'd ever dreamed," said Henderson, who suddenly found herself dealing with the rich and powerful. She had few orders, however, from "everyday dog lovers," a clientele she was anxious to reach. By attending dog grooming conventions and holding pet fashion shows, Henderson has since met with smaller retailers. Now her coats are available from Massachusetts to California. A few of the more interesting ensembles are a ruffled red satin tango outfit, a Sherlock Holmes coat and hat, quilted down coats and shearling-lined raincoats.

"The sizes range from an 8, which is a chihuahua, to a 36, which is a Great Dane. Coats are priced from $7.50 to $3,800 depending on the design, materials, and custom-make." Henderson says the secret of her success is simple. "People love their dogs. There is a need to express the love felt for a pet. When someone buys a cashmere coat for their dog, they are not displaying their wealth but their love."

One New York client, who wanted a touch of elegance for the mating of his dogs, had Henderson design a white marabou and satin cloak for the "bride" and tie and tails for the "groom." Only in New York? Well, in Los Angeles a Doberman pinscher attended his master's wedding in a specially designed white tie and tails with a tiny satin pillow on the shoulder -- he was the ringbearer.

When asked about cats, Henderson says, "Cats hate to be dressed. Try it sometime." As for other house pets, she has made exceptions. One client asked for a white mink coat for his parrot, and got it. "I couldn't resist the challenge," Henderson laughs.

In town last week to attend a Baltimore pet show and to see some "very, very private clients," Henderson would not reveal the names of embassy-related customers who feared for their pets' safety. "After all," she said, "a pet owner who would pay several hundered or even a thousand dollars for a custom-made doggie coat would be a dog-naping risk."

Between visits with very important dog owners, Henderson did get a chance to go to the theater. What did she see? "What else . . . 'Cats.' "