LAKE FOREST, Ill. – Leave it to Mike Brown to deliver one of the bigger hits from the Chicago Bears recently.

While the slate gets wiped clean following Thursday’s preseason finale at Cleveland, Brown made no effort to hide his concern after watching the defense fall flat against San Francisco in a 37-30 loss last week. Just an exhibition? Don’t tell him that.

“That’s not an excuse,” the former Pro Bowl safety said.

It didn’t rank up there with Brown saying his team stinks after a 1-3 start in 2005, but the message was clear. If the defense is going to carry the Bears again, improvement is needed.

That was evident last Thursday.

After containing Kansas City and Seattle, the Bears’ starters could not hold the 49ers in check despite an unsettled quarterback rotation and the absence of three starting linemen and three wide receivers. The worst offense in the league last season, San Francisco, quickly jumped on the Bears (0-3 preseason) while piling up 27 points against the first-teamers in the first 2 1/2 quarters.

The Niners’ Frank Gore cut through a big hole on the first play from scrimmage for an 11-yard run and did it again on the second play, this time sidestepping Brian Urlacher on a 28-yarder.

Then, Urlacher got sealed off on a 16-yard run by Zak Keasey on the fourth play, putting the ball on the Chicago 16.

General manager Jerry Angelo showed his faith in the offseason by giving Urlacher, defensive tackle Tommie Harris and defensive end Alex Brown contract extensions while re-signing linebacker Lance Briggs even though the defense took a big step back last season.

Chicago allowed 354.7 yards per game and ranked 28th overall while managing just 33 takeaways last season after leading the NFL with 44 in 2006.

“I’m always concerned if we’re not performing the way we’re supposed to be, but I’m confident that we’re capable of doing it, of being a dominant defense and we will be,” Briggs said.