CARSON, Calif. - After getting ready with exhibitions against three top-10 opponents, the United States opens World Cup qualifying tomorrow against Barbados, a team tied for 121st in the FIFA rankings.

Although the United States is heavily favored in the home-and-home series, which concludes June 22 at the Caribbean nation, forward Landon Donovan cautioned that qualifying matches can be difficult.

"Mentally, if you're not ready for these games, these teams can jump on you," said the 26-year-old Donovan, a veteran of two World Cups. "You can expect that every one of those teams that we're going to play against is going to be ready to play. If you're not ready, you're going to be in for a dogfight."

The United States, seeking its sixth straight World Cup appearance, had a first-round bye in the North and Central American and Caribbean region. Barbados beat Dominica 2-1 in their series.

Three teams from the CONCACAF region will qualify for the 2010 World Cup in South Africa, and the fourth-place team will play the No. 5 nation from South America for another berth.

The American team, currently ranked 21st, has changed since a disappointing showing in the 2006 World Cup in Germany, when it was bounced out in the first round with a 3-0 loss to the Czech Republic, a 1-1 tie with Italy and a 2-1 loss to Ghana. The United States finished tied with Iran for 25th in the 32-nation field. Coach Bruce Arena was replaced by Bob Bradley after negotiations with Juergen Klinsmann broke down.

"Everybody understands the importance of these games," Bradley said. "The national team schedule is a unique one for any country and we are always excited when we have a chance to work together and, obviously, play important matches."

The Americans are coming off a 2-0 loss at No. 9 England, a 1-0 loss at No. 4 Spain and a 0-0 tie against top-ranked Argentina.

Thirteen of the 21 players on the preliminary roster, which will be trimmed to 18 before the match, have experience in qualifying. But younger players have been added, with Freddy Adu, Michael Bradley (son of the coach), Dominic Cervi, Maurice Edu and Sacha Kljestan all under 23.

Bradley sees qualifying as a maturing process for the national team.

"You need younger players with the experience to continue to improve," he said. "You need to feel that your key players are taking more and more responsibility, not only on the field but off of the field in terms of their leadership. It's really about growth. As we start this two-year period, we understand that World Cup qualifying is always a challenge and you have tough games along the way."

The United States beat Barbados 7-0 at Foxborough, Mass., and 4-0 on the road in 2000, during qualifying for the 2002 World Cup.

"You've got to have a certain balance of experienced players and young players who are hungry. I think we have a good balance of that," said midfielder DaMarcus Beasley, back from a knee injury that sidelined him from late November until mid-May. "We're not the finished product by a long shot; we're still in somewhat of a rebuilding year."

Barbados, which is expected to play a defensive game, has brought nine players in from overseas, including Marcel McKie, Paul Ifill, Mark McCammon, Johnathan Forte and Jonathan Nurse from England.

"We need to be the aggressor," U.S. defender Steve Cherundolo said. "In any home-and-home series, it's important to have a good, solid first game."

If the Americans advance, they would be in a semifinal group that likely will include Cuba, Guatemala, and Trinidad and Tobago.

"We have players that have been through qualifying and understand what it's like, and never to take any opponent lightly," Bradley said. "You can tell that in the last few days as we've switched gears from this three-game stretch of playing top teams to World Cup qualifying. You constantly hear Landon Donovan, Timmy Howard and Carlos Bocanegra and others talking to their teammates about what to expect, and how the first game is key, and how we're home and what we need to do early in the game."