The Seahawks are usually very set with their roster by this time of the offseason, having already retained their key free agents, perhaps added a couple and then of course drafted.

But this year is different: They should be very active in the so-called Phase 3 of free agency, because they still have not improved their defensive line.

The Seahawks have ditched their top three pass rushers over the past two offseasons, and the only notable guy they have added to replace them is first-round pick L.J. Collier. And he alone will not add up to a Frank Clark, Michael Bennett or Cliff Avril.

Thankfully, Pete Carroll and John Schneider plan to do more.

“We talk about those phases of free agency,” Schneider said. “There’s basically like three or four different phases, and we’re basically now heading into Phase 3.”

“We’re very much involved with what’s coming up next,” Carroll said. “We’re not done. We’ve got work to do, and we’re excited about what’s coming up. You guys will see in time.”

With Bennett, Avril and Clark gone, the Seahawks have no fully proven pass rushers. Collier joins backups Cassius Marsh and Jacob Martin as Seattle’s top outside rushers. It’s a sorry state of sackers.

Jarran Reed had 10.5 sacks last season, from the inside, but everyone is waiting to see whether that was an anomaly or his new normal.

The Seahawks need help wherever they can get it — and that should mean adding as many as three veteran defensive linemen.

The top veteran outside rushers available are Nick Perry, who is coming off a knee injury, and Ziggy Ansah, who is recovering from a shoulder injury. Both have visited Seattle (Ansah on Monday), and both would come with risk. The Hawks also might consider cheaper 30-somethings Derrick Morgan or Connor Barwin.

The best inside players available are Ndamukong Suh, an Oregon native who talked to Seattle last year and prefers the West Coast, and Muhammad Wilkerson (though he is expected to re-sign with Green Bay after he recovers from an ankle injury).

Seattle also wants to add a veteran run stopper. The Hawks have talked with Earl Mitchell, Allen Bailey, Corey Liuget and Al Woods. Danny Shelton is still out there, too. They are very likely to sign one of those guys to help a run defense that gave up 4.9 yards per carry (third worst in the NFL) in 2018.

Perry could be signed now, but most of those veterans would not be added until after May 7, when the COMPetition ends. It is very possible the Hawks have wink-nod agreements with a couple of them already.

Another avenue Schneider could explore is trading. He has plenty of ammo — 11 picks — from the 2020 draft.

Trade rumors swirled around the 49ers’ Solomon Thomas and the Jets’ Leonard Williams after those teams drafted similar players in the top three Thursday. But both GMs shot down the ideas.

Maybe Schneider could try to get someone like Buffalo’s Jerry Hughes or the Colts’ Jabaal Sheard for a mid-round pick (both the Bills and Colts drafted pass rushers). Or maybe Tampa tackle Gerald McCoy.

Not counting Doug Baldwin’s expected credit (around $7 million), the Seahawks have about $22 million for veteran additions, so they feasibly could add three linemen — maybe paying Mitchell $2 million, Perry $5 million and Suh $8 million or acquiring McCoy (whose salary is $10 million) or Hughes ($6.5 million).

Whatever the combination, it is clear the Seahawks must add at least a couple of good linemen if they are going to have a chance to be much better than they were last year.

“We’re not done. John’s got a lot of stuff he’s working on,” Carroll said. “The next couple of weeks will be really exciting for us.”