Harper will be on the taxi squad, which means he will play twice per week. When he doesn't play, Harper will work on his swing and his skills in the outfield.
The news comes after Harper hit .319 with a .407 on-base percentage for the Nationals in the instructional league. He also led the team in several offensive categories, including hits, homers, RBIs and walks.
"He performed admirably in the instructional league," general manager Mike Rizzo said. "He got his feet on the ground and he was immersed in baseball, which he embraced greatly. He is what we call a baseball rat."
Rizzo said he thought about putting Harper in the AFL before the young slugger started playing in the instructional league, but he didn't make the decision until recently. Rizzo said Harper's performance on and off the field reinforced his decision.
"He's 17 years old and he doesn't even turn 18 until Saturday," Rizzo said. "He is very excited. What I had to decide on was: 'Is he going to be over his head in the AFL?' It's a very advanced league, but I think he is going to handle it. It's going to be very valuable to him."
The club did not want Harper to be idle for the next two months, so they believed it was better for him to continue playing baseball under Randy Knorr, who is managing the Scorpions. Knorr is considered one of the best teachers in the Nationals' organization.
Rizzo, Nationals manager Jim Riggleman, hitting coach Rick Eckstein and Phil Rizzo, a special advisor to the general manager, will also be in Arizona to help develop Harper.
"There is a high level of baseball going on," Mike Rizzo said. "Two months of this guy working out, practicing and playing will only benefit him. He is going to be fine in the [AFL]."
Harper is expected to begin the 2011 season at Class A.
"He is going to A-ball, make no mistake about it," Rizzo added. "He is not going to be a rushed guy. We are going to let his performance and development dictate where this guy goes."
Harper, after putting up monster numbers in high school, received a lot of publicity last year when Sports Illustrated referred to him as the "Chosen One," and baseball's version of LeBron James.
Shortly thereafter, he turned more heads when he received his high school equivalency in lieu of becoming a junior in high school, then headed to the College of Southern Nevada to join a junior-college program that plays in a wooden-bat conference.
Having been used primarily as a catcher in the past, Harper is currently playing right field. Rizzo believes that Harper will get to the big leagues faster if he plays somewhere other than behind the plate. He is considered an above-average outfielder with a great throwing arm and speed.
In addition to the physical tools, Harper had the stats to warrant being taken No. 1 overall. In 2008 as a freshman at Las Vegas High School, Harper had a .599 batting average with 11 home runs and 67 RBIs in 38 games. He followed that up with a .626 batting average, 14 home runs and 55 RBIs the next season.
Playing against a high level of competition and hitting with a wooden bat didn't present much of a challenge to Harper. The 17-year-old hit .442 with 29 home runs and 89 RBIs during the 2010 regular season.
Bill Ladson is a reporter for MLB.com and writes an MLBlog, All Nats All the time. He also can be reached on twitter -- @washingnats. This story was not subject to the approval of Major League Baseball or its clubs.