PERHAPS IT is a swan-song melody.

Maybe it is a lame excuse.

It might just be the truth.

Besieged coach Andy Reid acknowledged yesterday that the Eagles' most glaring weakness results from the inexperience of its defense's core.

And, hey, what coach can be held responsible for youth? The Eagles had designs on the Super Bowl but stand at a devastatingly disappointing 4-8 . . . with an error-prone, skittish group supporting the defensive line.

The most frequently used linebackers and safeties, five players, have a combined 78 career starts among them. They are Jamar Chaney, Moise Fokou, Brian Rolle, Nate Allen and Kurt Coleman.

Defensive tackle Mike Patterson has 96 by himself. Defensive end Trent Cole has 94. Cornerback Nnamdi Asomugha, 110.

"I understood that we were going to be young up the middle, and our primary concern is to ensure that we're going to continue to get better," Reid said. "So that's what we're working on doing."

They are working with little success. Led by former offensive-line coach Juan Castillo, who compiled or inherited a rebuilt defensive staff, and Eagles rank 17th in yards allowed, 22nd in points allowed and, most significant, dead last in red-zone efficiency.

All of which has caused the rabble to call for the head of Reid, Castillo and, if possible, the six-fingered murderer from "The Princess Bride."

Does Reid fear for his future? Is there truth to a report that Reid has been issued an edict by the front office to fire Castillo to save himself?

"There is nothing there," insisted Reid, whom the Eagles owe $10 million over the next two seasons.

As young as the five players in question are, there are other issues.

For one thing, the lockout cost the league its offseason work - crucial when installing a new scheme with a new staff.

Allen, a second-year safety, is only 1 year removed from a season-ending knee injury, which cost him the first three starts of the season. Five players have shared various linebacker duties; none of them has started in the same position all 12 games.

Chaney, who played middle linebacker at the end of last season as a rookie, is the only one among the five core players in question who has started every game. Even Chaney's year has been muddled: He began as the strongside linebacker and switched two games into the season after fourth-round rookie Casey Matthews was moved, first from middle to weakside, then, a game later, to the bench.

Chaney's head is swimming.

"I had to learn the MIKE last year in a different system, then I spent this training camp learning the SAM," Chaney said. "Then, during this season, I had to learn the MIKE in this system."

"We are improving," Allen said. "Learning from our mistakes."

If anything, Reid and perhaps Castillo miscalculated the young players' learning curves - though, when asked, Reid would not say so explicitly. He offered more platitudes about hoping to improve.

Which, also, might just be the truth.