Culture : Off the Rack : From royalty to pretenders, everyone who’s anyone knows where to get outfitted for Ascot.

The glittering crowd in the Enclosure during Royal Ascot Week, which begins today, will include tastefully turned out aristocrats, millionaires, American tycoons and a charlatan or two.

But there’s one thing many of the gentry will have in common: They’ll have rented their fancy cutaways and top hats from a London firm known to everyone as Moss Bros--where the abbreviation for brothers rhymes with Moss.

Moss Bros will tog out nearly 10,000 patrons of the thoroughbred track this week, the beginning of England’s summer social season. Some outfits are rented out twice, and even three times, during the racing week. Wise customers have reserved their morning coats well in advance.

Moss Bros not only rents the styles, it helps set them, with a keen eye on society’s pacesetters. For instance, the establishment maintains close ties with Buckingham Palace to make sure it is on the royal wavelength in sartorial matters.

The actor Anthony Hopkins, awarded a knighthood by the queen, stopped by Moss Bros to make sure he was properly attired.

Most recently, the palace passed the word to Moss Bros that at next month’s wedding of Lady Sarah, Princess Margaret’s daughter, black morning gear would be appropriate.

Black was also the designated cutaway color at the wedding of the Prince and Princess of Wales, but Diana’s father, Lord Spencer, insisted that he would wear gray--and did.

“The customer is always right,” murmured a Moss Bros executive of Spencer’s outfit.

Thus Moss Bros is suitably represented at Royal Ascot, weddings, a royal garden party, a ball, or a white tie-and-tails dinner.

“Our head fitter, Roy Weston, can make anyone look good,” said corporate consultant Colin Woodhead, pointing to the fitting rooms where customers waited patiently, first-come, first-served, for Weston’s talents.

“He can size you up coming in the door. There’s no one he can’t fit. Moss Bros would never let anyone leave the premises unless his kit could pass royal inspection.”

In fact, many in the royal Establishment rent or buy their own formal wear from Moss Bros, and many wealthy patrons who could easily afford to purchase morning suits prefer to hire, officials say, noting that the price of a new three-piece morning suit runs from $750 to $3,000.

American customers can line up their outfits in advance.

Ken Ward runs a travel agency in Atlanta that takes a party of 10 to 15 people on a weeklong house party for Royal Ascot every year.

“We order by fax,” Ward said. “They can make hired suits look custom-made. They have never let us down.”

The classic morning wear, with a black herringbone cutaway coat with dove gray waistcoat and striped trousers, runs about $60 for 24 hours--with shirts, ties and shoes additional.

Although it maintains a more traditional line of clothing, Moss Bros claims to be the largest renters of formal wear in the world. But it got into the “hire” line almost by accident.

The company was founded in 1851 by Moses Moss, who opened a men’s clothing shop in Covent Garden, Central London’s vegetable, fruit and flower market, and also the home of the Royal Opera House. His policy: “Giving good value and selling good stuff.”

By the turn of the century, the business had grown, moved to larger quarters down the street (it now has branches in dozens of British cities) and was taken over by the founder’s two sons, George and Alfred Moss, where it acquired its distinctive Moss Bros name.

The brothers introduced the first ready-to-wear, or “off-the-peg,” suits for the rising middle class--at a time when all men’s attire was custom-made.

In the Edwardian era, at the beginning of this century, Moss Bros became the place to buy all manner of special attire for royal, diplomatic, military and formal occasions, and its fame spread.

“People knew that if they had been invited to a special event in Britain, they would always be properly advised and attired if they had been to Moss Bros,” Woodhead said.

In 1897, Alfred Moss had a friend of good social standing who had lost his fortune as well as his white tie and tails.

To maintain his social standing, he needed a dinner outfit, and Moss lent him one from the store. After a time, the friend borrowed the dinner outfit so often that Moss asked him to pay something toward its care--and they settled on a modest sum and so created the first formal-wear hire service.

When the friend regained his fortune, enough to own a whole wardrobe, he still chose to “hire” from Moss Bros since he knew that his tails would be cleaned, pressed and immaculate.

Morning dress, which is compulsory in the Royal Enclosure at Ascot, with the tail coat, waistcoat (vest) and striped trousers, was what most British gents wore every day 100 years ago.

They would change into white tie and tails for dinner.

But the lounge or business suit became popular for daytime wear, and the white tie was fossilized with the advent of the black-tie dinner jacket--popularized by Americans belonging to a country club at Tuxedo Park, N.Y., hence the name.

As day dress became more informal, the tail coat and top hat remained the correct dress for special occasions. And Moss Bros stood ready to supply.

One commentator at the coronation of King George VI in 1937 said there was so much Moss Bros stock worn by those taking part, from dukes to coachmen, that it could not have taken place without the company’s products.

Moss Bros clientele have included such celebrities as cowboy actor Tom Mix, composer Sir Edward Elgar, playwright Noel Coward, impresario Mike Todd, designer Valentino and British Cabinet members.

In World War II, Field Marshal Bernard Law Montgomery and U.S. Gen. George S. Patton were customers for custom-made uniforms. And a back room at Moss Bros was secretly used to create authentic French clothing for spies parachuted into occupied France.

These days, Moss Bros is more focused on weddings than war. Modern brides are demanding that the participants in their rites hire from the experts.

“Part of the reason for the increasing use of formal wear at weddings,” Woodhead said, “is the videocorder. People like to film weddings and they want action. Since they are filming, they are the stars--and want to be dressed like stars, once in their lives.”

The comeback of formal wear is reflected in the Moss Bros Group, which includes Cecil Gee and Savoy Tailors Guild stores. Group sales last year were up 11% over 1992, profit climbed, and the outlook remains promising.

“I think our rental department has contributed much to our overall success,” Woodhead said. “It has given us a can-do corporate culture like the Americans. . . . “

As an afterthought, he added: “Funny. After a wedding, the item most often found in the returned garment is a marriage certificate.”