The club exercised its option to extend Acta's deal beyond the 2008 season because he improved the Nationals' record by at least one game with a three-game weekend series at Philadelphia to end the regular season.
As the series begins, Washington is 72-87, compared to last season's 71-91 mark under Frank Robinson.
"I don't think I have learned as much as I’m being reassured of the plan that I had put together in my mind over the last five years," the 38-year-old Acta told the Washington Post.
"I think he's the best young manager in the game," said General Manager Jim Bowden.
"He's highly intelligent. He's well prepared (and) he's a good motivator. He’s a good leader. . . . I think he runs a good game, and I think he’s a winner."