Detroit made the moves Monday before coach Matt Patricia and team executives answered questions from season-ticket holders at Ford Field.
Longa had a season-ending knee injury last year during the preseason after being a key player on special teams for the Lions in 2017. Longa played in one game in Detroit in 2016 after being signed by Seattle as an undrafted free agent out of Rutgers.
The Lions claimed Loewen off waivers from New Orleans in December. The former Arkansas standout played in three games for the Saints over the 2017 and 2018 seasons.