The NFL’s most explosive offense served the Kansas City Chiefs well in the 2003 regular season. Then came the playoffs: Peyton Manning and the Colts knocked them out in their first game because their defense didn’t stop the Colts at all.

What did the Chiefs do to fix it?

They kept the same players and brought in Gunther Cunningham, their former head coach (and defensive coordinator before that), to fix the schemes that weren’t working under the fired Greg Robinson.

The approach differed in Denver, where the normally offensive-minded Broncos went for defense, giving up Clinton Portis, a 1,500-yards-a-season running back, to get shutdown cornerback Champ Bailey.

Oakland, which went from the Super Bowl to 4-12 last season, is trying to get back with veterans Warren Sapp, Ted Washington and perhaps Kerry Collins.

San Diego? It’s hard to tell if the Chargers are really trying.

The Chiefs scored 484 points last season, or more than 30 a game as quarterback Trent Green, running back Priest Holmes, and tight end Tony Gonzalez had their way behind a standout offensive line. Return man Dante Hall, meanwhile, terrorized opposing special teams with four early touchdown returns, plus one in the playoffs.

They covered up the defensive problems during a 9-0 start. But the trouble became evident late in the season. The Chiefs lost three of their final seven, then failed to stop the Colts and lost 38-31 in their first playoff game.

Enter Cunningham, who will do what most teams do when a unit fails – change the system, in this case, go from “read and react” to attack.

“I think it’s going to be a different attitude and a different atmosphere and they’re going to play a lot better this year,” Gonzalez said. “It’s all of us together, putting it together and trying to get this going.”

The only question on offense is at wide receiver, where Johnnie Morton and Eddie Kennison are just OK and Hall operates as a sometime deep threat. The offensive line might have problems if perennial Pro Bowlers William Roaf (34) and Will Shields (almost 33) begin to show their age.

The defense needs more from the front seven, especially third-year tackle Ryan Sims, a high draft pick who has yet to be better than ordinary. It also will likely be without middle linebacker Mike Maslowski, who has been slow to recover from knee surgery.

Denver has always won with offense – coach Mike Shanahan made his reputation there and still is considered one of the game’s best innovators.

But this year, the Broncos are concentrating on defense, especially in the secondary.

They were willing to give up Portis to get Bailey – contract issues on both sides also came into play – and signed veteran Pro Bowl safety John Lynch after he was released by Tampa Bay. The trade of Portis happened in part because Denver has always been able to plug in unheralded running backs to get big yardage: Terrell Davis, Olandis Gary, Mike Anderson and even Portis, a second-round pick.

This year, it will be Quentin Griffin and rookie Tatum Bell, although Denver was dealt a major blow when Anderson, now the fullback, was lost for the season with a groin injury. Another bad omen: veteran defensive tackle Luther Elliss has a torn pectoral muscle, the same injury that troubled him the last few years in Detroit.

Jake Plummer was effective when healthy in his first season as Denver’s quarterback and the Broncos still have one of the game’s best offensive lines. Rod Smith, at 34, has some mileage on him, but remains a dangerous receiver. It would be nice if Ashley Lelie, now in his third season, can show more than flashes of brilliance.

Still, the main addition is Bailey, who the Broncos think can make a difference in a defense that was embarrassed 41-10 in its wild-card playoff game in Indianapolis. On one play, three Broncos DBs stood around watching while Marvin Harrison, who was never touched when he fell to the ground after catching a pass, casually got up and ran 30 more yards for a touchdown.

“A guy like Champ is as close to a shutdown corner in this league as there is,” says Collins, who played against Bailey when he was the Giants’ QB. “He’s the kind of guy who can take a receiver out of the game.”

Right now, Collins is out of the game in Oakland, backing up 38-year-old Rich Gannon, who missed nine games last season with a shoulder injury. But that could change. Collins has been impressive in exhibitions and he is owner Al Davis’ kind of QB, big with a very strong arm.

Also in Oakland are Sapp and Washington, veterans obtained to bolster the middle of the defensive line. Tim Brown was released and signed with Oakland East in Tampa Bay, but Jerry Rice, who will turn 42 on Oct. 13 – he led the team with 63 catches in 2003 – is back for his 20th season.

On paper, San Diego did well in the draft, getting a bunch of extra choices in the trade with the Giants that brought them Philip Rivers for Eli Manning. But typical for the Chargers: Rivers was a holdout until three days before the third exhibition game and is likely to start the season behind Drew Brees.

The only bright spot there is LaDainian Tomlinson, perhaps the most complete running back in the game. He even signed a long-term contract extension that probably means he will spend the rest of his career with the franchise.

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Predictions: Denver 11-5; Kansas City 10-6; Oakland 6-10; San Diego 4-12.

AP-ES-09-01-04 1343EDT