Disappointing the queen and leaving expatriate American jockey Steve Cauthen far behind, Britain's defending riding champion Willie Carson steered big, handsome Troy from the middle of the pack to an impressive seven-length triumph today in the 200th running of the Epsom Derby, the world's richest and most historic thoroughbred classic.

Only the failure of the sentimental favorite, Milford, owned by the queen and ridden by eight-time Derby winner Lester Piggott, Britain's premier jockey, blemished an otherswise fitting bicentennial of the venerable stakes race for 3-year-olds. Named for one of its founders, the 12th earl of Derby, it has spawned more than 200 similar racing classics round the world, including America's Kentucky Derby.

The winner's purse today of more than $300,000 was a world's record, and the finish was international. Troy, at odds of 6 to 1, was followed by Irish-trained Dickins Hill at 15-1, French-owned Northern Baby at 66-1, and the 9-2 favorite, Ela-Mana-Mou (Greek for Come On, My Darling), owned by a Greek Restaurateur's wife here.

The crowd covering the natural amphitheater of gently rolling green hills around the race course at Epsom Downs, 16 miles southwest of London, was estimated at between 300,000 and 500,000, easily the largest for a sports event in Britain. And the sun shone brightly all day on what always has been as much a festival for residents of London as a classic horse race, with its midway of amusement rides and games of chance, beer tents and champagne picnics, traditional gypsy caravan and colourful royal procession.

With Queen Elizabeth II, Prince Philip and Crown Prince Charles watching from the clubhouse with other nobles, notables, horse owners and guests, the men in morning dress with tails and top hats, jockey Piggott tried gamely to give the queen the second royal win in Derby history.

Milford, starting on the inside of the crowded 23-horse field, hung a promising second just behind pace-setting longshot Lyphard's Wish much of the way around the undulating, horse-shoe-shaped grass course. But he faded back out of the money going down the long, sloping straightaway toward the finish of the 1 1/2-mile race.

That was when Carson, in all-white silks atop Troy, seemingly trapped near the rail in the middle of the still-bunched pack, almost miraculously made his way between horses to the outside. Once clear of the pack, Troy exploded past the tiring leaders and continued accelerating through the uphill finish. His dramatic burst of late speed in the otherwise rather slow running produced the biggest winning margin in more than 50 years.

Cauthen was never in contention with Tap On Wood, the horse he expertly rode to a narrow victory in the 2,000 Guineas, the first race in Britain's triple crown, highlighted by the Derby and concluded by the St. Leger Stakes. Cauthen said after the race that he was never able to get Tap On Wood running up the hill and into the left-hand turn in the first half of the race.

Cauthen, who continues to be a favorite with bettors and the press here after arriving earlier this year to ride for English horse owner Robert Sangster, impressed the huge crowd at Epsom earlier in the day by easily winning the Daily Mirror Handicap aboard Philodantes. His later poor showing in the Derby with a smallish horse that clearly did not have the strength for Epsom's ups and downs was no disgrace.

Carson's Derby win was his first in 11 tries.

The 200th Derby was also history and spectacle. It has been promoted here in books and souvenir novelties, numerous television and radio special programs, and a "Derby Day 200" exhibition at the Royal Academy of London of paintings and memorabilia from two centuries of the Derby, including the preserved tail of the 1865 winner, Gladiateur.

It was begun by the young 12th Earl of Derby and horse-owning friends in 1780 at Epsom, where the race course for the thoroughbreds of royalty and gentlemen began as an adjunct to a fashionable 17th century spa. The mineral springs there added "epsom salts" to the English language.

As the spa's popularity dwindled, interest in racing grew and the gentlemen's bets on the outcome attracted enterprising intermediary oddsmakers first known as "blacklegs" and only much later as "bookmakers." Although their activites would lead eventually to today's worldwide business of pari-mutuel, tote and off-track betting, they were in the early 19th century notoriously dishonest fly-by-night types who fixed a number of early Derby races, including at least one won by a 4-year-old under an assumed name.

The race attracted everyone who could get out of London for the day, both the aristocrats who bought tickets for the grandstand and the common folk who have never had to pay to occupy the hillsides around the course. Catering to their desires for food, drink, entertainment and various games of chance in the carnival atmosphere of "London's unofficial holiday festival" are the great families of gypsies who have traditionally gathered at Epsom for Derby week, once in ornately painted horse-drawn wagons, now in glistening motorized campers.

But the sleaziness and occasional thievery and violence that lurked around the edges of the derby never kept either the crowds or notables away. Dickens came to write about it. Degas, Dufy and Pollard, among others, came to paint the scene. Royalty, led by Edward VII, Queen Victoriz's playboy son, raced their horse in the Derby. Edward's won three times, twice while he was crown prince and once while he as king, in 1909.

The contrast between the regal pageantry and sweaty carnival was again evident today the 200th Derby.

While Queen Elizabeth, in matching peach-colored gown and hat, led the royal procession from clubhouse to grandstand to see her horse before the race, her subjects rode on the Ferris wheel and merry-go-rounds and played the games of chance in the amusement area, got drunk on beer and champagne and sun-bathed on the hillsides, and surveyed the scene from open-topped double-decker buses chartered for the day. CAPTION: Illustration, One man's idea of how a race between the cream of the decade's racing crop would shape up: Seattle Slew and Affirmed break on top, Slew holds lead after a mile but tires, Secretariat turns on gas and flies by Spectacular Bid and Affirmed and hits the wire a solid two lengths ahead of "Bid," with Affirmed another three lengths back. By Alice Kresse - The Washington Post; Picture 1, Secretariat; Picture 2, Spectacular Bid;