IT IS ONE OF BASEBALL'S most time-tested truisms: If you want to be a good team, you've got to be strong up the middle. You only have to look to Citizens Bank Park to see proof of that claim.

But baseball isn't the only sport where the "strong up the middle" axiom is essential to success. It's also pretty damn important in football.

Look under the hood of any top NFL defense and you'll usually find a couple of hard-to-budge, run-stopping tackles, a play-making middle linebacker and two very good, smart, athletic safeties.

The Eagles had all of the above last season, which is a big reason they finished in the top five in just about every significant defensive category, including third in total defense and points allowed.

Brodrick Bunkley and Mike Patterson excelled against the run as the Eagles held 11 of their 16 regular-season opponents to double-digit rushing yards.

In just his second NFL season, Stewart Bradley established himself as one of the league's top young MIKE linebackers. And safeties Quintin Mikell and Brian Dawkins teamed up for 311 tackles, five sacks, four interceptions, eight forced fumbles, one Pro Bowl invitation (Dawkins) and one second-team All-Pro selection (Mikell).

But Dawkins is gone, signing with the Denver Broncos, and Bradley was lost for the season in early August when he tore the anterior cruciate ligament in his right knee.

Suddenly, a defense that was rock-solid up the middle last year isn't so.

There's still Bunkley and Patterson up front, and Mikell at strong safety. But with the season opener against the Carolina Panthers just 4 days away, they've got major question marks at both middle linebacker and free safety.

The two options at MIKE - Joe Mays and Omar Gaither - both have their flaws. Mays is a physical, downhill player, but was inconsistent in the preseason and struggled in coverage. Gaither started 16 games at MIKE in 2007. He's smart. He's technically sound. But he's not a physical player.

As for Dawkins' old free safety spot, well, the Eagles thought they had two pretty good options there in '08 fourth-round pick Quintin Demps and former Cleveland Brown Sean Jones, whom they signed as a free agent.

But Demps has talked a better game than he's played. He made mistake after mistake in training camp and the preseason - missed tackles, blown coverages, repeatedly being out of position.

Jones was a strong safety in Cleveland, but the Eagles' safety positions basically are interchangeable. Mikell essentially was a free safety last year after Jim Johnson moved Dawkins up closer to the line of scrimmage to maximize what he still did well (play the run, blitz) and minimize what he didn't (coverage). But Jones has struggled to get his arms around the Eagles' defensive scheme.

That apparently leaves fifth-round rookie Macho Harris, who opened training camp as a cornerback and now seems to be defensive coordinator Sean McDermott's choice as the Week 1 starting free safety.

"You lose Bradley in the middle and now you've got concerns about the middle part of your defense deep," an NFL pro personnel executive said. "That would concern me. If I'm an offensive coordinator playing the Eagles, I'm going to be trying to attack them in the passing game in between the numbers."

The Panthers favor the run. They finished third in the league in rushing last season and ran the ball nearly six more times a game than they passed. But that ground success makes them a dangerous play-action team.

"The main thing we've got to go out there and do Sunday is we've got to stop the run first," said defensive end Juqua Parker. "Once we stop that, we can get them in situations we like to play in, where we can rush the passer. If we don't do that, it could be a long day. But as long as we get out there and we stop the run, we can control the game."

In his defense, Gaither did a pretty good job against the run in his 16 starts in the middle in '07. Led a defense that finished seventh against the run in tackles. He just doesn't have the size you'd like in a MIKE and doesn't spend nearly as much time as you'd like on the other side of the line of scrimmage. He had just four tackles for losses in '07.

Mays probably is a better option at MIKE against the run. The problem is, opposing coaches and quarterbacks aren't stupid. You put a guy who's a liability in coverage out there on first and second down and guess what? They're going to throw at him. You saw that in '06 with Jeremiah Trotter when he couldn't move anymore. He might as well have had a big red "X" on his jersey.

"Losing Bradley was costly," another pro scout said. "He was a really good player who could do a lot of different things. Now you've kind of got to mix and match. It's going to be very important for [strongside linebacker Chris] Gocong to play well and for [weakside linebacker Akeem] Jordan to play well."

Only time will tell how much the Eagles will miss Dawkins. He turns 36 next month and isn't the player he once was. That said, my guess is that, right now, McDermott wishes he could send him out there to play free safety on Sunday rather than the inexperienced Harris or the undependable Demps or the befuddled Jones.

"You're taking a boundary corner and asking him to play safety," the first scout said of Harris. "I like the kid. He's a baller. I can't speak to the mental side as far as being able to make the adjustment. But I don't know if he has the natural instincts to be a safety. If he's going to start Week 1, boy, that's asking a lot." *

Send e-mail to pdomo@aol.com