Jonathan Daniel/Getty ImagesThe Bears' defense is spending more time on the field with the offense's struggles.

LAKE FOREST, Ill. -- Bears linebacker Brian Urlacher and the rest of the defense continue to avoid the temptation of lamenting the offense’s dismal third-down numbers over the past four games, which seem to make it increasingly difficult to neutralize opposing offenses.

Over the past four weeks, Chicago’s offense has converted 11 of 50 on third-down conversions, after moving the chains on 22-of-52 attempts the previous four weeks with Jay Cutler at quarterback.

“We can’t let it get to us,” Urlacher said. “Our mindset is [to] go back out there and take the ball away for our offense. That’s all we can do; just go out there and try and get three and outs ourselves or take the ball away. We don’t think about it. I mean, we have a hard enough time ourselves. We can’t be worried about what happens on offense.”

But it’s affecting what takes place on the other side of the ball. In the first half of Sunday’s loss to Seattle, the Bears’ defense was on the field for 29 snaps, with the unit holding the Seahawks to only one TD on a possession that started at the Chicago 22 because of a Johnny Knox fumble.

In the second half, Chicago’s defense worked for 36 Seattle snaps, resulting in 17 points. One of the Seattle scoring drives in the second half started at the Chicago 29, after Leon Washington returned a punt 36 yards.

After finishing the first half 3 of 6 on third down, the Bears never made another third-down conversion.

Urlacher said the defense “just fell apart in the second half,” but teammate Lance Briggs characterized it differently.

“I don’t think there was necessarily a letdown [late in the loss to the Seahawks],” Briggs said. “It’s more of a letdown in our discipline, in things we normally would be able to handle.”

Apparently, the defense’s ability to deal with the offense pulling it into arduous situations is waning as the team approaches the conclusion to the regular season. Nickel cornerback D.J. Moore said the “offense will do fine,” adding that “whatever happens, we just know we’ve got to play good on defense.”

He’s correct. But at some point, the offense needs to put the defense in an advantageous situations with sustained drives. The defense put a touchdown on the board for the Bears in the first half, only to watch the offense give back two more touchdowns on interceptions returned for scores.

“We have to outplay [the other team’s] defense every week. That’s one of our goals,” said Bears defensive coordinator Rod Marinelli. “We’ve got to make sure we’re working hard to get the takeaways and scoring on defense. That’s important for us.”

It’s also paramount the defense ignores the team’s ineptitude on offense. That’s precisely what defensive end Julius Peppers said the unit plans to do in its attempt to focus in on Green Bay’s high-flying offense, led by quarterback Aaron Rodgers and a bevy of weapons at the receiver positions.

“We’re not concerned with what the offense is doing,” Peppers said. “We’ve got to play better ourselves.”