A COUPLE OF WEEKS back, just before free agency started, Tra Thomas talked about the possibility that the Eagles were going to wind up changing both starting offensive tackles. The notion seemed odd at the time - you knew it could happen, but after a franchise-record 134 games of Thomas on the left side and Jon Runyan on the right, it was hard to envision, like, say, Brian Dawkins signing with Denver.

"That would be a lot of change," Thomas agreed, if neither he nor Runyan returned. "That would be throwing a lot on [offensive line coach Juan Castillo's] shoulders."

There's a lot on Castillo's shoulders this morning.

Yesterday, Thomas, 34, signed a 3-year deal with the Jacksonville Jaguars. Financial terms weren't disclosed, but were thought to be relatively modest. Runyan, 35, rehabbing from microfracture surgery aimed at creating cartilage in his right knee, sits on the free-agent market, where he is likely to stay at least a few months, until he can work out and satisfy teams that he can play again. When that happens, the Eagles could be among the interested parties, but their one big free-agent signing was a right offensive tackle, Cincinnati's Stacy Andrews, so Runyan's chances of reclaiming his job don't look great.

Contacted last night, Runyan didn't want to talk about his situation, but he mentioned in a text message that he is counting down the weeks until he gets off crutches. He's still a couple of weeks away.

"Waiting for Week 8 to come so I can get on the road to recovery!" Runyan texted.

The Eagles made an offer to Thomas before free agency, one agent Peter Schaffer was unenthusiastic about. Thomas told WIP Radio yesterday it was for a 1-year pact. The Birds seemed to have gone into free agency thinking there was a good chance they would still retain Dawkins. That clearly was not the case with Thomas; they had plenty of time to woo back the man who protected their quarterback's blind side for his first 11 seasons, making the Pro Bowl three times. They clearly chose to move on.

The question is, move on to what? Left tackle generally is considered the most important (and undeniably is the best-paid) of the o-linemen. The Eagles once were grooming Winston Justice as Thomas' successor, but they don't even try to pretend that anymore - they moved Justice to the right side last year and apparently have been trying to trade him.

Eagles coach Andy Reid has discussed two scenarios - Reid thinks right guard Shawn Andrews, Stacy's brother, might have been the best collegiate tackle he ever saw, before the Eagles traded up to draft him from Arkansas in the first round in 2004. And Shawn, speaking to reporters on a conference call the day Stacy's signing was announced, spoke of taking sets on the left side this offseason. He remarked on how natural that felt.

Shawn Andrews did not return messages from the Daily News yesterday.

Reid also has spoken of moving left guard Todd Herremans outside. Reid's preference is to draft tackles and turn them into guards who can play tackle if need be. He did that with Shawn Andrews and with Herremans. But what sort of NFL left tackle would Herremans be - does he have the quickness to move outside? He certainly doesn't have Thomas' NBA-level wing span; when Herremans came out of Saginaw Valley State in 2005, draft reports mentioned his short arms.

"They're the longest pair I've ever had," Herremans observed yesterday, after a NovaCare workout. "Juan talked to me about that after I was drafted. I guess I do have a little bit of short arms, by NFL tackle standards. He said that just means you use different techniques - your feet definitely have to move a little quicker; your timing's got to be better."

Herremans said he definitely thinks he could play left tackle, if that is what the Eagles want. He said he hasn't heard anything - nobody has asked him to start breaking down film of defensive ends.

Herremans texted Thomas yesterday to congratulate him on the new deal. Herremans said he wasn't terribly surprised by the upheaval, given the tackles' age and their free agency. He said he thought one reason the Birds have been a little young at the inside positions in recent years is that the coaches knew the tackles wouldn't be around a lot longer, and they didn't want to have to change the whole group.

If Herremans moves outside, who would take his current spot? Stacy Andrews began his pro career as a left guard, and played very well there. That could leave an opening for Runyan's return, or Shawn Andrews could slide out to right tackle. Backup center Nick Cole was a good right guard fill-in last season, when Andrews and Max Jean-Gilles were injured, and Cole could probably start there.

Of course, the Eagles also have 12 picks in next month's entry draft, including two in the first round. They absolutely will draft some o-linemen high, though whether those players can help next season is hard to say.

In a Jacksonville news conference, Thomas acknowledged he didn't have a lot of suitors, though he is thought to have been responsible for only two sacks last season.

"Really not that many were biting at me. Once I came here and visited with [general manager] Gene [Smith] and the offensive line coach, Andy [Heck], I knew that this was going to be a perfect fit for me," he said.

Thomas, who is from DeLand, Fla., about 100 miles from Jacksonville, has often maintained that he wants to play 20 years.

"I have several years left in the tank. I take good care of myself; I'm always in the weight room training," he said yesterday.

Thomas was asked whether he was surprised the Birds didn't try harder to keep him.

"Not really. It was a shock to me, but I'm glad this worked out," he said, in a bit of a non-sequiter.

The Eagles released statements from team president Joe Banner and from Reid extolling Thomas' contributions to the team.

"During his 11 years in this city, he's been nothing but a true professional and leader, both on and off the field," Reid said. "Most importantly, he's a proven winner in the National Football League and will go down as one of the finest offensive tackles in the history of the Philadelphia Eagles. We wish he and his family all of the best in Jacksonville."


The Eagles announced they re-signed exclusive-rights free agent Tank Daniels and claimed running back Eldra Buckley off waivers from San Diego. *

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