The Nationals have been interested in Guardado, 39, since the Winter Meetings. According to the source, team scouts told general manager Mike Rizzo that Guardado would be a big help to the club.
Rizzo was unavailable for comment.
Nicknamed "Everyday Eddie," Guardado is considered a workhorse out of the bullpen. During his 17 seasons in the big leagues, he has played in 908 games and saved 187 of them. He is best known for his years as the Twins' closer. His best season was in 2002, when he saved 45 games and posted a 2.93 ERA.
Guardado is not expected to close for the Nationals, however. Instead he is expected to be a mentor as well as a setup man.
Guardado will become the second reliever acquired by the Nationals this offseason. Washington traded for right-hander Brian Bruney on Dec. 7, and will find out on Wednesday if free-agent reliever Matt Capps will sign with the club.
Capps will sign with either the Cubs or Nationals, according to his agent, Paul Kinzer. If the Nationals acquire Capps, he will battle Bruney for the closer role.
The Nationals have been in need of bullpen help. This past season, Washington relievers posted a 5.09 ERA, the highest in the Major Leagues.
Bill Ladson is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.