Ruud adds a veteran presence to the Seahawks' young linebacker corps and replaces David Hawthorne, who signed with New Orleans on Tuesday.
Ruud played nine games for the Tennessee Titans last season before being placed on injured reserve with a groin injury. Ruud had 57 tackles and one interception for Tennessee. He played his first six NFL seasons with the Tampa Bay Buccaneers.
Lutui played for coach Pete Carroll at USC before spending the past six seasons with the Arizona Cardinals. Lutui potentially could challenge for the starting job at left guard after the release of Robert Gallery last month.
Lewis has played the past three seasons in Seattle, primarily as a nickel back and special teams standout.
He was the special teams captain in 2010 before a knee injury landed him on injured reserve. The injury lingered into last season as he landed on the physically unable to perform list for the first six games. Lewis appeared in 10 games for Seattle and recorded 20 tackles last season.