LAKE FOREST — The Chicago Bears defense has been good — even very good — the past three weeks. But the leaders on the ‘D’ believe they could have, and still should, do more.

LAKE FOREST — The Chicago Bears defense has been good — even very good — the past three weeks. But the leaders on the ‘D’ believe they could have, and still should, do more.

“We can always play better. Playing better means finding ways to win, not giving up late touchdowns or letting the other team drive down the field 90 yards,” linebacker Lance Briggs said.

“It’s all part of these next three games, and giving ourselves a chance to get into the playoffs.

To do that, the Bears will have to win at least two of their last three, and most believe that includes Seattle (6-7) on Sunday.

Chicago (7-6) has dropped three in a row to fall behind in the race for the final wild-card spot. The statistics say little blame can go to the defense, which has allowed just three touchdowns during that three-game skid.

The Bears defensive stars say something else, however.

“If we don’t win, then we haven’t done enough as a defense,” defensive tackle Anthony Adams said.

“Stepping up should translate into wins, so we’ve got to do what we got to do to win out. Anytime you lose and anytime you play so well but there’s just a couple of breakdowns here or there, it always leaves a bad taste in your mouth.”

When quarterback Jay Cutler went down with a thumb injury on Nov. 20, Pro Bowl linebacker Brian Urlacher said they expected the defense to “step it up from here on out.”

Since then, Chicago has held its opponents to an average of 312.7 yards and 16 points while forcing four turnovers. But the offense has averaged just 275.7 yards and 11 points and has coughed the ball up seven times.

Still, the defense refuses to call out the offense, insisting they themselves still haven’t done enough.

“Obviously not. We’ve lost all three games, so no, we haven’t done enough,” Urlacher said. “We just haven’t played well enough to win. It doesn’t matter what happens on the other side of the ball for us.”

The biggest issue defensively has come down to one big series or play.

Chicago held Oakland to six straight field goals in a classic bend-but-don’t-break effort on Nov. 27.

But an 8-play, 74-yard drive that was capped off by the Raiders’ only touchdown of the day proved to be the backbreaker in the fourth quarter.

During a 10-3 home loss to Kansas City, the Bears surrendered a 38-yard Hail Mary touchdown on the last play of the first half.

Last weekend’s debacle in Denver saw the Bears shut down Tim Tebow and the Broncos’ attack until the final four minutes of regulation and overtime.

That’s when Tebow lit up the Bears, completing seven fourth-quarter passes in a row to kick-start the Broncos’ rally, and leading three straight scoring drives to close it out.

“We have to do more to win those games,” Urlacher said, “and we haven’t done that.”

Bears reporter Jay Taft can be reached at 815-987-1384 or jtaft@rrstar.com.