CHICAGO – Goalkeeper Tim Howard, defender Carlos Bocanegra, midfielder Michael Bradley and striker Clint Dempsey were among 16 players called into training camp on Tuesday to prepare for the U.S.’s World Cup qualifiers next month.

The team will train at the ESPN Wide World of Sports Complex in Orlando, Fla.

Tuesday’s call-ups consists mainly of foreign-based players who have completed their seasons and are ready to prepare for the series of matches that culminates in the team’s first qualifier against Antigua & Barbuda in Tampa, Fla. on June 8. The Americans play at Guatemala on July 12.

As many as 13 additions will be announced May 20 and will be a mixture of domestic and foreign-based players to round out the training camp.
The team will train in Orlando until May 25, when Klinsmann will select a final 23-man roster for the upcoming five matches. The group then departs for Jacksonville, Fla. in preparation for the match on May 26 against Scotland (8 p.m. ET, NBC Sports Network, Galavision). The team will host a public training session May 25 at EverBank Field .

“All the players coming now for this very special four-week period represent our core,” Klinsmann said. “It’s a clear signal to other players that right now it’s down to business. We’re playing World Cup qualifiers. It’s not about experimenting or seeing different players, it’s about who we think are the best. We are excited to start with this first group of players, and then welcome more at the beginning of next week. It’s the first time we will have our best players together for a longer stretch of time, so we have a chance to work very hard and go out and get results.”

Dempsey has a minor groin injury, according to Klinsmann, who won’t push the Fulham player in the early stages of camp.

“Clint has a minor groin injury which should be fine within the next couple of days,” he said. “We’re going to take it a bit easy in the beginning, and from there we don’t expect any problems.”

Defender Timmy Chandler declined an invitation to attend camp. The 22-year-old Chandler, a starter for Nuremberg in the Bundesliga, made his U.S. international debut in March 2011 and has eight international appearances.

“He feels at this point he needs to take a break,: Klinsmann said. “It’s disappointing not having him as a part of the team at this important juncture., but ultimately a player must decide what is best for him. The door is certainly not closed on Timmy, but in the moment we move on without him.”

Klinsmann stressed that the time to experiment is over. It’s time to get down to business.

“All the players coming now for this very special four-week period represent our core,” he said. “If tomorrow was the World Cup, this is the group that comes in for our World Cup roster. It’s a clear signal to other players that right now it’s down to business. We’re playing World Cup qualifiers. It’s not about experimenting or seeing different players, it’s about who we think are the best.”

Real Salt Lake goalkeeper Nick Rimando and midfielder Kyle Beckerman were the only domestic-based players seleted on Tuesday.

The first 16 players called into camp:

GOALKEEPERS (3): Brad Guzan (Aston Villa), Tim Howard (Everton), Nick Rimando (Real Salt Lake)

DEFENDERS (4): Carlos Bocanegra (Rangers), Edgar Castillo (Club Tijuana), Steve Cherundolo (Hannover), Alfredo Morales (Hertha Berlin)

MIDFIELDERS (8): Kyle Beckerman (Real Salt Lake), Michael Bradley (Chievo Verona), Joe Corona (Club Tijuana), Maurice Edu (Rangers), Fabian Johnson (Hoffenheim), Jermaine Jones (Schalke 04), Jose Torres (Pachuca), Danny Williams (Hoffenheim)

FORWARDS (1): Clint Dempsey (Fulham)

Clint Dempsey has a minor groin injury. Andy Mead/YCJ