ST. LOUIS — The Cowboys and Rams have swapped underachieving former first-round picks, with offensive tackle Alex Barron going to Dallas and linebacker Bobby Carpenter headed for St. Louis.

Carpenter made only two starts in four seasons for the Cowboys, one in the regular season and one in the playoffs, and was a backup inside linebacker in a 3-4 defense last season. The Rams have a 4-3 defense and the 250-pound Carpenter could start.

Barron was the 19th pick of the 2005 draft and has made 74 starts for St. Louis but has been at least a mild disappointment. The Rams drafted Rodger Saffold of Indiana to open the second round of this year's draft and could start him at one tackle opposite Jason Smith, the second overall pick of last year's draft.

The trade was finalized Monday.