Nationals RHPJason Marquis was traded Saturday to the Arizona Diamondbacks for 21-year-old minor league infielder Zachary Walters, who is hitting .302 for Class A South Bend this season. (Rob Carr/GETTY IMAGES)

With the trade deadline looming Sunday at 4 p.m., the Washington Nationals dealt two veterans Saturday in order to stock their farm system and worked toward landing General Manager Mike Rizzo’s top priority of a long-term solution in center field.

Saturday morning, the Nationals traded utility player Jerry Hairston to the Milwaukee Brewers for Class AA outfield prospect Erik Komatsu. In the evening, they traded Jason Marquis — Saturday’s scheduled starting pitcher — to the Arizona Diamondbacks for Class A switch-hitting middle infielder Zachary Walters. Marquis was replaced with Yunesky Maya for Saturday night's game against the New York Mets.

Rizzo’s primary aim, however, remains acquiring a center fielder capable of filling an area the Nationals have lacked since the team arrived in Washington in 2005.

Their main targets are Denard Span of the Minnesota Twins and B.J. Upton of the Tampa Bay Rays, with Span seemingly the more likely player to end up with the Nationals.

The Twins and Nationals have been discussing a possible deal involving closer Drew Storen, according to a person with knowledge of the situation. The Twins, according to another person, have insisted that Nationals outfielder Roger Bernadina also be included in a deal for Span.

Rizzo did not explicitly rule out trading Storen, but he considers him part of the Nationals’ “core” and would be loath to lose him. Still, trading a reliever — even a closer under team control for another five seasons — for an everyday center fielder who leads off, like Span, may be too tough for Rizzo to pass up if he can strike a deal with the Twins.

“Drew Storen would be a very difficult person to trade,” Rizzo said. “He’s a 23-year-old, terrific closer. He’s very dear to our hearts here, because we drafted him, signed him and developed him. He’s definitely a core piece, and he would be very difficult to trade.”

In return for Hairston, the Nationals received Komatsu, 23, who was drafted in the eighth round of the 2008 draft. At Class AA Huntsville this season, Komatsu has hit .294 with a .393 on-base percentage and a .416 slugging percentage. He has six home runs and 13 stolen bases.

Komatsu, the Brewers’ minor league player of the year in 2010, has drawn wide praise for his ability reach base: He has more walks (121) than strikeouts (105) over the past two seasons. But he projects as a solid fourth outfielder in the majors — he is not quite fast enough to play center field, and does not hit for enough power to play every day in a corner outfield spot.

Hairston, 35, filled a versatile, valuable role for the Nationals this season, acting as the regular third baseman when Ryan Zimmerman missed two months with a torn abdominal muscle. He also played left and center field and came off the bench as a right-handed pinch hitter. Hairston hit .268/.342/.385 with four homers and two stolen bases in 75 games.

“Having him around helped me tremendously,” Nationals shortstop Ian Desmond said. “There’s been a couple times that maybe he saw that I was down, or see saw something in me that he wanted to pull me aside and talk to me. It’s easy to listen to a guy like that. He’s been through everything.”

Since the Brewers and Nationals exchanged no cash in the deal, the Brewers will pay the remaining $650,000 of Hairston’s one-year, $2 million contract.

In trading Marquis, Rizzo found a partner willing to give up both a minor leaguer and assume the roughly $2.3 million remaining on Marquis’s contract, a two-year, $15 million deal he signed before the 2010 season. Marquis went 8-5 with a 3.95 ERA this season, the consistent performance the Nationals hoped for when they signed him. In his first season in Washington, Marquis developed bone chips in his right elbow and went 2-9 with a 6.60 ERA in just 13 starts.

The Nationals scouted Walters, 21, heavily leading up the 2010 draft, because he played on the same team at the University of San Diego as Sammy Solis, their second-round pick that season. He is batting .302/.377/.485 this season at Class A South Bend with nine homers and 12 stolen bases.

The Nationals were motivated to trade Marquis not only to add another piece to their farm system, but also to make room in their rotation for right-hander Brad Peacock and lefty Tom Milone, their two top pitching prospects at Class AAA Syracuse. The Nationals planned for Maya to make only one start.

The Nationals plan, as of now, to bring Peacock to the majors first. They want both him and Milone to experience the majors leagues this season to see how they respond and to prepare them for next season, when they will compete for rotation spots in spring training.

Trading Marquis on the day of his scheduled start created an odd scene in the clubhouse. broke the news of the trade at around 5 p.m. About a half-hour later, Marquis sat on a stool in front of his locker and told teammates, “They haven’t told me anything.” Soon, they did, and after a year and a half with Washington, Marquis readied to fly into a pennant race.

“Last year was a little frustrating,” Marquis said. “I had to do a lot of work to make sure when I came back I would be the old Jason Marquis. This year turned out the way I wanted it. I’m throwing the ball the way I want. It’s an exciting time to know a team has enough confidence in you to be a part of a postseason run.”

The rest of the Nationals just played the Mets. Some of them, with the deadline less than 24 hours away, had to wonder if they would be next.

“This is so much easier in a video game,” Storen said.