By Robert Millward

Associated Press

PHOTOS BY ASSOCIATED PRESS >> Freddy Adu, left, and Michael Bradley are two of the young players the U.S. is counting on to produce some success in the 16-team field.

LONDON >> Despite being the world’s most popular sport, football usually takes a back seat at the Olympics, dwarfed in terms of importance by athletics, swimming and even gymnastics.

Even though megastars such as Ronald-inho and Lionel Messi are going to China, the spotlight won’t really swing toward them until the final stages.

Yet Olympic football was making waves a little more than two weeks before it starts on Thursday. A series of ugly rows developed during the buildup with clubs refusing to release their stars even though they have been called up by their countries searching for an elusive gold medal.

The clubs’ argument is that it’s another irrelevant and badly timed tournament, while the International Olympic Committee and soccer’s world governing body FIFA are trying their best to give football a bigger impact in the Games.

For decades it was played by so-called amateurs and dominated by teams from the former Soviet bloc because the big stars from western countries, who were paid, weren’t allowed to take part.

Now the Olympics are open to professionals in all sports, and football is for teams of players who are age 23 and under with three overage stars allowed to join them. The prospect of winning an Olympic gold medal has prompted some of the big names to join their rising stars and, while 21-year-old Argentina star Messi falls into the age category, 28-year-old Ronaldinho has decided to join the Brazilian squad to try to add another title to his already impressive record.

With 16 teams taking part and a final in the Olympic stadium Aug. 23, the IOC and FIFA hope that soccer will maintain its growth within the Olympics after stand-out performances in recent years by gold medal winners Nigeria (1996), Cameroon (2000) and Argentina (2004).

Freddy Adu, Jozy Altidore and Michael Bradley will lead the U.S. men’s soccer team.

Forward Brian McBride, goalkeeper Brad Guzan and New England Revolution defender Michael Parkhurst are the three overage players allowed in the under-23 tournament.

Selecting the Olympic squad was tricky because the Beijing Games overlap with World Cup qualifying for the U.S. team.

“We’re trying to accommodate the Olympic team, but we need to also keep in mind it’s an important time for the senior team,” coach Peter Nowak said. “We need to make sure we field two competitive teams.”

The 36-year-old McBride is the veteran of three World Cups. He retired from international soccer in 2006 and left Fulham of England’s Premier League in May, but agreed to help the U.S. team in the Olympics.

Guzan, who turns 24 in September, is transferring from Chivas USA in Major League Soccer to English club Aston Villa. He was the 2007 MLS Goalkeeper of the Year. Nowak said Guzan was committed to playing for the U.S. in the Olympics and that Aston Villa was cooperative.

The Americans open Olympic play Thursday against Japan.