Kansas City, Mo ? Kansas City was undefeated in its first nine games, but the Chiefs were 4-4 in their last eight.

It was a startling decline, the sort of thing to be expected when a wave of injuries strikes a team.

Only that isn’t what happened. The Chiefs were remarkably healthy throughout a 13-3 regular season, and put more than half their offensive starters in the Pro Bowl, including kick return wizard Dante Hall.

So what was the problem?

In a word: Dee-fense!

For the second straight year, coordinator Greg Robinson’s defense collapsed at the wrong time, capped by a 38-31 loss to the Indianapolis Colts in Sunday’s AFC divisional playoff game.

The porous defense offset just about everything the Chiefs’ high-powered offense produced. All year, the offense ranked at or near the top of the NFL in points and total yardage, but the defense was Kansas City’s downfall.

This year, Priest Holmes bounced back from hip surgery and scored an NFL-record 27 touchdowns. Hall emerged as the most electrifying return man in the game, returning kicks for TDs in a record four straight games during the regular season and then adding a fifth with a 92-yarder against the Colts.

Six offensive players are headed to the Pro Bowl — quarterback Trent Green, guard Will Shields, tackle Willie Roaf, tight end Tony Gonzalez, Holmes and Hall.

The only defensive player headed to Hawaii is safety Jerome Woods.

Again, the Chiefs’ offseason mission will be to upgrade the defense, and for coach Dick Vermeil to decide whether Robinson returns next season.

“We know where the problems are, and we’re going to address them and get after it,” general manager Carl Peterson said.

So will there be coaching changes?

“That’s going to be up to the head football coach,” Peterson said. “I’ve left that up to him.”

Vermeil, 67, decided on New Year’s Day that he was returning next season, and possibly for another. He and Peterson are close friends going back to the early ’70s at UCLA. Peterson has two more years on his contract and many believe the two could go out together in 2006.

But of immediate concern is defense. The Colts, who had 434 yards, no turnovers and no offensive penalties, were not the only team to shred Robinson’s unit.

In the Chiefs’ last two road games, Denver and Minnesota each scored 45 points.

As the players took their physicals, met with Vermeil and departed Monday, they were noncommittal about changes for next year.

“On paper, (the defensive talent) is very impressive,” said defensive end Vonnie Holliday, one of three newcomers brought in last year. “As far as what changes need to be made, I’ll just leave that up to coach Vermeil.”

The Chiefs are in good shape salary cap-wise. Their only free agent on offense is right tackle John Tait. Woods and Greg Wesley, the other starting safety, are both free agents, as is defensive end Eric Hicks and defensive lineman John Browning. Woods and Browning are expected to exercise an option to void their final year.

But the Chiefs have been working hard to whittle “dead money” off their payroll and now have only about $4 million they’re paying out to players no longer with the club.