It's easy to look at the Eagles' defense with an optimistic eye as the team prepares to close out its season Sunday against the Buffalo Bills.

To see the half-full glass, consider how far the defense has come in a year - while getting younger.

When the Eagles finished the 2006 regular season, the defense was 15th in the NFL in yards allowed, tied for 15th in points allowed, and 26th in rushing yards allowed. With just one game to go this season, the Eagles are ninth in yards allowed, 11th in points allowed, and fifth in rushing yards allowed.

"It's exciting," defensive coordinator Jim Johnson said yesterday. "We have a bunch of young guys. I like our front, and we've got some linebackers producing. We'll just have to make sure we have everybody back and healthy and we'll go from there."

To see the half-empty glass, examine the turnovers and the yards allowed in the passing game. The Eagles have forced just 19 turnovers in 15 games, the fewest in the NFL and a major reason they are minus-6 in the turnover differential. Only 11 teams have committed fewer turnovers than the Eagles' 25.

The Eagles' 11 interceptions are tied for the fewest in the league. If they don't get at least two against the Bills, it will be the team's lowest total since 1998, when coach Ray Rhodes' 3-13 team had just nine.

Seven players have started in the secondary, but cornerback Lito Sheppard doesn't think that's a legitimate excuse.

"It's the turnovers, and I'm a big part of that," Sheppard said. "My big plays are definitely down this year."

The Eagles rank just 20th in yards allowed through the air.

On the positive side, it could be argued that the Eagles got younger and better at four starting positions on defense while two other young players - defensive tackle Mike Patterson and defensive end Trent Cole - displayed tremendous improvement.

Brodrick Bunkley, 24, has replaced Darwin Walker, 30, as the starting right defensive tackle. Juqua Thomas, 29, has replaced Jevon Kearse, 31, at starting left defensive end. Both have played major roles in the Eagles' drastic improvement at stopping the run, the defense's biggest weakness a year ago.

Johnson will spend much of the off-season deciding how to use his linebackers, who were a big question mark when the season opened and are now considered a strength.

Omar Gaither, 23, replaced Jeremiah Trotter, 30, as the starting middle linebacker, and Chris Gocong, 24, replaced Dhani Jones, 29, as the starting strong-side linebacker. Both proved to be upgrades.

Takeo Spikes, one of just two defensive starters older than 30, did a solid job at weakside linebacker, but there's some question about how he will fit in next season. Rookies Stewart Bradley, 24, and Akeem Jordan, 22, created the question by playing solidly Sunday against New Orleans.

"It's a good problem to have," Johnson said. "I think it's something you have to evaluate at the end of the season. Maybe we'll go to a 3-4, who knows?"

Johnson was only half joking about a 3-4, because he has used that alignment a few times this season, starting with the game at New England, in which he allowed Gocong to become a pass rusher with his hand down for the first time all season.

"I think there's going to be plenty of opportunities to mix and match as far as the personnel groups, having both Omar and Stewart on the field at the same time," Johnson said.

In passing situations against the Saints, Gaither moved to weakside linebacker, the position he played last season, and Bradley was in the middle. In the base defense, Jordan played weakside linebacker and Gaither was in the middle. When Gaither left Sunday's game in the third quarter with a quadriceps injury, Bradley played middle linebacker and Jordan played on the weak side.

Johnson wants Spikes back.

"No question about it," Johnson said. "He wants to be back. He's a good player and he had a good year for us."

He also is scheduled to make $5 million next season, which could be a factor in the Eagles' decision-making if they think Bradley or Jordan can do the job as well as or better than the veteran.

The bigger problem for Johnson likely will be the secondary. The defensive coordinator said Joselio Hanson had earned the right to be the third cornerback, but he will be a restricted free agent.

"I think he's one of our solid players right now," Johnson said. "He's done a great job for us. He's not a really big guy, but he plays hard and is a good cover guy."

Asked about Sheppard, Johnson gave a different answer.

"I really don't want to get into that," he said before instructing the questioner to ask coach Andy Reid. "I don't know what we're going to do. I think we have to sit down at the end of the season and evaluate."

Sheppard, 26, has missed 13 games the last three seasons because of injuries, including four this year with a knee injury.

Of course, the Eagles also must decide how much veteran safety Brian Dawkins has left in the tank. Dawkins, 34, has missed five games this season, and it's questionable whether he will play in the season finale. He has just one interception and no sacks.

"I still think he has a year or two left in him," Johnson said. "The biggest thing with him, of course, is the off-season. As you get a little older, you really have to work a little harder in the off-season. He knows that. He's ready to go."

Johnson was comfortable with the rest of his safeties but wouldn't be surprised if the Eagles tried to upgrade at that position.

"I think that Q has done a great job," he said, referring to Quintin Mikell. "It's going to be an interesting thing when Sean Considine comes back. Great competition there. Marcus Paschal, a young safety we brought in, I like him. J.R. Reed has done a great job. I'm sure we're always going to look for good football players."

Contact staff writer Bob Brookover at 215-854-2577 or bbrookover@phillynews.com.