SAN DIEGO -- The Nationals exchanged outfielders with the Athletics on Wednesday evening, trading Chris Snelling to Oakland for Ryan Langerhans.

General manager Jim Bowden said he made the deal to improve the team's defense. The Nationals are last in the National League in that department. Langerhans is expected to be one of the club's reserve outfielders. Kory Casto is likely to be the other one when center fielder Nook Logan is taken off the disabled list.

"In our ballpark and with our young pitching staff, it's good to have good defense in the outfield. We want to be able to catch the ball," Bowden said. "Ryan can play all outfield positions, and he is a plus in all three positions. We thought that was important, especially in our ballpark."

This is the second transaction involving Langerhans in less than a week. On Monday, the Braves traded him to the A's for a player to be named later or cash considerations. It was a deal that left Langerhans in shock because he grew up in the Atlanta system.

Langerhans was in Boston when the second trade was announced, and he will join the Nationals on Thursday afternoon in Chicago. His best season was in 2005, when he hit .267 with eight home runs and 42 RBIs.

"I'm excited about joining the Nationals," Langerhans said via phone. "I was getting to know the players in Oakland. They are good guys, and I'm going to join good guys in Washington."

For the season, the left-handed-hitting Langerhans, 27, is a combined 3-for-46 with one RBI. Langerhans acknowledged that his swing was out of whack early in the year, but he feels he is back on track.

"I've hit the ball hard, but the hits haven't been falling," Langerhans said.

Langerhans, who is out of Minor League options, is expected to make $410,000 this season.

As for Snelling, he hit .204 with one home run and seven RBIs in 24 games with the Nationals after being acquired on Dec. 18, 2006, with right-hander Emiliano Fruto in exchange for second baseman Jose Vidro and cash considerations.

Bowden hinted that he still is looking to make trades. He is looking for a power hitter in the starting lineup and possibly a right-handed hitter off the bench.

Bowden did not say who he was interested in, but Red Sox outfielder Wily Mo Pena has been a player that has been on the Nationals' radar screen for months. Bowden always has believed that Pena could be another Sammy Sosa in terms of hitting a lot of home runs.