By Estelle Shirbon

LONDON (Reuters) - Brazilians in bikinis will replace soldiers in bearskin caps when Olympic beach volleyball comes to Horse Guards Parade, a London site normally used for the annual Trooping the Colour military ceremony marking Queen Elizabeth's birthday.

The choice of venue may not be as incongruous as it first seems, for beach volleyball and Trooping the Colour have at least one thing in common: the participants' outfits are a big part of the spectator appeal.

The game invented on the sunny coast of California made its official Olympic debut in 1996 but still draws scoffs from purists who question whether a sport played on beaches by women in skimpy swimsuits deserves a place in the Olympic schedule.

Whatever the rights and wrongs, beach volleyball is a major draw and the iconic location, a stone's throw from the prime minister's office at Number 10 Downing Street, is sure to enhance the spectacle -- weather allowing.

There are two medal events: the men's and women's competition. The 24 teams in each event will first compete in a group stage and 16 will progress to the knockout stage.

In keeping with their rich beach cultures, the United States, Brazil and Australia dominate the sport and are the only three nations to have won Olympic gold.

The U.S. women's pair of Misty May-Treanor, 34, and Kerri Walsh, 33, are the only team to have won Olympic gold twice. After Athens and Beijing, gold in London would elevate them to the status of legends of the sport.

"It would be a great way to leave the game," May-Treanor told Reuters this month. She plans to retire from competition after the London Olympics.

Since the last Games, May-Treanor ruptured her Achilles tendon rehearsing for the hit TV show "Dancing With The Stars" while Walsh gave birth to two sons less than a year apart. But they have not lost their competitive instincts.

"We have been setting standards for others to follow and setting records that may be unbroken. These are great things but we want to be a legendary team, untouchable," said May-Treanor.

Other top contenders are the reigning world champions, Brazilians Larissa Franca and Juliana Felisberta, and Bejing bronze medalists Xue Chen and Zhang Xi of China.

The three top-ranked teams in the men's game are Emanuel Rego and Alison Cerutti of Brazil, Todd Rogers and Phil Dalhausser of the United States and German pair Julius Brink and Jonas Reckermann.

The collective challenge for all beach volleyball players at these Games is perhaps to display sporting prowess so stunning as to silence the sniggers. Even Britain's former Prime Minister Tony Blair has been known to make a beach volleyball joke.

"It is a masterstroke by the organizers to site the beach volleyball in Horse Guards Parade, just outside the prime minister's window," Blair once said, although he is no longer in office to enjoy the show.

(Editing by Peter Rutherford)