Watched by U.S. President George W. Bush, the U.S. Olympic delegation entered the opening ceremony of the Olympic Games on Friday night.

The United States, which sent 596 athletes to Beijing, is defending its medal supremacy for the fourth consecutive time in face of severe challenges from China and Russia.

The Americans regained the lead in the gold medal table in Atlanta in 1996 when they beat archrival Russia 44-26 in golds, and they continued to dominate the table in the following Olympics held in Sydney and Athens.

The United States took 97 medals in Sydney in 2000, including five won by Marion Jones.

Jones admitted being a dope cheater last year and was stripped of her three golds and two bronzes by IOC this year and sentenced to prison for six months.

The California-based Bay Area Laboratory Co-Operative, also known as BALCO, had supplied a number of high-profile sports stars from the United States and Europe with THG and growth hormones for several years.

The BALCO customers are included famous sprinters Jones, Tim Montgomery, runner Regina Jacobs, hammer thrower C. J. Hunter, boxer Shane Mosley and hundreds of players of American professional league, such as MLB well-known player Barry Bonds and NFL player Bill Romanowski.

Victor Conte, founder and president of BALCO, entered guilty pleas in July 2005 and was sentenced to spend four months in prison and another four on house arrest.

"The things you are hearing about are from a previous era. We're in a new era," said USOC chairman Peter Ueberroth, organizer of the 1984 summer Olympics held in Los Angeles and chaired USOC in 2004.

To rebuild the new era of the Americans' sports, Ueberroth swore solemnly to send a "clean team" to Beijing during the USOC Media Summit in Chicago this April.

"This will be a clean team," Ueberroth said. "We're proud of the progress we've made in doping. There's no way to guarantee anything, but we feel very good about this team."

While battling the continuing problem of drugs domestically, the Americans will not give up their medal supremacy to their arch rivals China or Russia this time in Beijing with ease.

"The excitement that is behind the team comes first of all with Russia, China and the U.S., with all three having a legitimate shot vying for at the top gold and total medal count," said Steve Roush, USOC's chief of sport performance.

"I think it has created excitement around these Olympic Games that has maybe been missing for awhile."

The Americans topped the gold race with 36 in Athens four years ago while China ranked second with 32 golds, just four fewer than the U.S. team. Russia won 92 medals, 10 fewer than the United States.

"We're forced," said Roush. "China has an incredibly strong team. Host nations generally have home field advantage."

"We have a good team. We have a strong team. We believe that the Chinese have the strongest team," USOC chief executive Jim Scherr said.

(Xinhua News Agency August 8, 2008)