Outfielder Roger Bernadina will also participate, playing for the Netherlands, in the event that begins March 2.
"The little kid in me wanted to say, 'Yes,' right away without thinking it through," Detwiler said of receiving the invitation and discussing it with the Nationals' brass. "But I came in, we all thought it through, and it was still a yes, so I'm happy about that."
Detwiler, 26, won a career-best 10 games for the Nationals last year and posted an ERA of 3.40. He is expected to be Washington's fourth or fifth starter this season. He also donned the USA jersey in the 2006 World University Baseball Championship in Cuba.
"It was amazing and we actually won the championship," Detwiler said. "I have the ring on my nightstand, so I see it every night when I'm at home. It's amazing, somebody asking you to represent your country playing baseball."
Gonzalez also was a late addition to Joe Torre's staff, but will not join the club unless it reaches the second round of pool play in Miami. Nationals manager Davey Johnson has said he wants Gonzalez to get three Spring Training starts with Washington before leaving for the World Baseball Classic.
"It's great," Detwiler said of having Gonzalez along with him. "It kinda calms you a little bit. We'll be in untested waters. Having somebody there that I was with all year last year is gonna kinda calm me down a little bit, and it's gonna make it seem like a regular start."
Gonzalez is slated to pitch on Monday, Feb. 25, March 2 and 7, leaving him in line to pitch on March 12 for Team USA, which would be the first game of the second round at Marlins Park.
Detwiler will make his first Spring Training start with the Nationals on Feb. 26, throw again on March 3, and then likely debut for Team USA on March 9 in pool play against Italy in Phoenix.
"We feel it's our duty and obligation to put the best team forward that we can for Team USA," Nationals general manager Mike Rizzo said. "We're honored that they want two of our starting pitchers to pitch for Team USA, and we're flattered about it. I know Ross is really fired up for it and he wanted to do it. We'll work around that schedule and we'll make sure he's prepared for our Major League season."