Frustrated by his offseason absences, concerned about some off-field issues and wary of a surgically repaired and still-balky back, the Miami Dolphins on Friday afternoon released six-year veteran defensive lineman Daryl Gardener.

To replace Gardener, who was scheduled to move from tackle to end this season, Miami also acquired defensive end Jay Williams from the Carolina Panthers. In return, Carolina received a fourth-round choice in the 2003 draft and defensive end Al Wallace.

Dolphins coach Dave Wannstedt said releasing Gardener "is in the best interest of the team.''

"The timing has a lot to do with being able to make the trade for Jay Williams,'' Wannstedt said. "After we made the trade, we assessed the team and made the decision that this was best for the football team.''

A first-round choice in the 1996 draft, Gardener and running mate Tim Bowens formed one of the NFL's biggest and best interior tandems the last few seasons. In six years, the mammoth Gardener often played at a Pro Bowl level, but was slowed by recurring back problems. He underwent surgery last year and played in just eight games.

Miami officials decided after the '01 season that it might be wise to move Gardener out to end, where he could play at a weight lighter than his standard 315 pounds, and exert less stress on his back. They also felt that, with the free agent departures of ends Lorenzo Bromell and Kenny Mixon, and the addition of tackle Larry Chester, the move would be a solid one from a competitive standpoint.

This offseason, however, Gardener, 29, missed enough scheduled workouts that he failed to qualify for a $200,000 bonus. That apparently was but one issue, though, in the club's decision to release him.

Between his scheduled $2.635 million base salary and various bonuses, the Dolphins will save over $3 million with Gardener's exit. He appeared in 82 games and started 77 times in six years, totaling 252 tackles and 15 sacks. But his value could not be measured just in statistics, because Gardener was effective in stuffing the inside running game and also protecting middle linebacker Zach Thomas.

In Williams, the Dolphins get a solid end who earlier this season appeared in trouble of being released by the Panthers for cap reasons, but who remained with the club after a meeting to clear the air. Williams, who was entering the final year of his contract, was scheduled to earn a base salary of $1.65 million. On Monday, the Dolphins signed him to a three-year extension through 2005. Terms were not disclosed.

League sources told ESPN.com that the Dolphins began making inquires on Williams a few days ago, but that it took the team teams a while to decide on compensation. At first, the Dolphins wanted to surrender only a low-round conditional draft choice. Williams will probably get first shot at the starting left end job.

The Dolphins earlier this spring signed veteran end Rob Burnett as an insurance policy.

The trade of Williams, 30, will clear the way for Panthers first-round draft choice Julius Peppers to assume the starting job at left end.

Williams has started 30 of 80 games in his career and has 79 tackles and 13 sacks. He had 13 starts in 2001 and posted 39 tackles and one sack.

Len Pasquarelli is a senior writer for ESPN.com. The Associated Press contributed to this report.