The Cowboys and the Packers. Mention the two teams, and your mind is flooded with images: The Ice Bowl. Lombardi and Landry patrolling the sideline. Bart Starr taking it himself, behind Jerry Kramer.

The Patriots and the Colts. More images, except these appear with the clarity of HDTV: Tom Brady taking a big early lead on Peyton Manning. Manning coming back and finally breaking through. Tony Dungy making history.

One rivalry is from a bygone era, 40 years ago. The other is a now rivalry, maybe the best in the NFL. Four weeks into the 2007 season, these four teams — the blue bloods and the nouveau riche — comprise the league’s elite.

The Cowboys, Packers, Colts and Patriots are the only undefeated teams, a Fab Four that is running away from the rest of the league. This was supposed to be a year of parity — wait a minute, that’s every year — but there seems to be a wide gap between the haves and the have nots.

That’s because some of the have nots were supposed to be haves. Five playoff teams from last season are off to miserable starts: the Bears (1-3), Chargers (1-3), Saints (0-3), Eagles (1-3) and Jets (1-3).

There has been no bigger disappointment than the Chargers, who fell to the Chiefs on Sunday, 30-16, after surrendering 24 unanswered points. For a team with so much talent, that is pitiful, and the home fans let them have it, chanting “Mar-ty! Mar-ty!”

That, of course, was an obvious reference to former coach Marty Schottenheimer, who was unceremoniously fired after last season because of his poor relationship with general manager A.J. Smith.

How’s that move looking now, A.J.? The Chargers already have lost more games than last season, with Norv Turner’s team slipping into a free-fall.

“They pay their money,” LaDainian Tomlinson said of the fans’ ire. “They have a right to voice their opinion. They showed their frustration with us, the way we’ve been playing. I can’t say that I blame them.”

It’s shocking to think that teams as good as the Chargers, Saints and Bears are a combined 2-9. All three teams are getting awful quarterback play from Philip Rivers, Drew Brees and Brex Grieseman, the two-headed monster in Chicago.

The Eagles have more mood swings than a daytime soap. One week after scoring 56 points, they allowed 12 sacks in a Sunday night loss to the Giants.

The Jets? They had high hopes for their second year under the “Man-genius,” the coach who made a brief cameo as himself in the penultimate episode of “The Sopranos,” but their defense is hiding somewhere in the witness protection program.

Let’s drop down to the bottom level, where you will find three winless teams — the Saints, Dolphins and Rams. St. Louis is utterly pathetic, and things don’t look better as the injuries continue to mount.

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Meanwhile, there are four teams at 3-1, only one of whom was expected to be a strong contender: the Seahawks. The Steelers suffered a bad loss Sunday to the Cards, 21-14, but they have enough talent to rebound. The Lions and Bucs are flawed teams, but they play in the NFC, where you will find more blemishes than at a Clearasil convention.

Things could change in the coming weeks, but there seems to be a great divide in the NFL caste system. Some of it is due to injuries (see the Bears), some of it is due to quarterback instability (again, the Bears) and some of it is due to poor coaching (the Chargers). Whatever it is, there seems to be a distinct separation.

There’s no doubt about the members of the select fraternity. Manning and the Colts are off to a great start, which is a dog-bites-man story. Brady and the Patriots, looking unstoppable, played Monday night in Cincinnati, where they rolled to a 34-13 victory.

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There’s no better story in the league than the Packers and Brett Favre, the aging gunslinger hoping for one last chance at Super Bowl glory. The Packers, sans a running game, are riding Favre’s legendary right arm, which belongs in the Smithsonian. He threw the 421^st and 422^nd touchdown passes of his career, breaking Dan Marino’s record.

“He’s playing at the MVP level that he played at before,” said Vikings safety Darren Sharper, who watched his former teammate throw for 344 yards Sunday.

Cowboys quarterback Tony Romo might be the new-age Favre, daring and exciting. He passed for 339 yards and three touchdowns to beat up on the Rams, helping the Cowboys to their first 4-0 start since 1995.

Romo’s signature play of the game — maybe his career — was something out of a Roger Staubach highlight film. He was 33 yards behind the line of scrimmage after retrieving a high snap, which he inadvertently booted, but he managed to turn it into a 4-yard gain. His teammates were awed by his improvisational ability.

How ‘bout them Cowboys?

“Four-and-oh is nice,” coach Wade Phillips said. “It doesn’t put us in the Super Bowl, it doesn’t put us in the playoffs. But it’s good that we’re there.”

They’re looking down at a lot of teams, and it’s a long, long way down.

NFL game stories Quick look at Week 4 games STEELERS 23, RAVENS 20, OT: Baltimore loses first game of season REDSKINS 26, COWBOYS 24: Dallas can't contain Portis in 1st loss BEARS 24, EAGLES 20: Goal-line stand boosts Chicago JETS 56, CARDINALS 35: Favre throws career-high 6 TDs BUCS 30, PACKERS 21: Ryan's 3 FGs lift Tampa CHARGERS 28, RAIDERS 18: San Diego tops rival 10th straight time BILLS 31, RAMS 14: Buffalo 4-0 for first time since 1992 CHIEFS 33, BRONCOS 19: Johnson rushes for 198 yards for K.C. BROWNS 20, BENGALS 12: Anderson throws TD TITANS 30, VIKINGS 17: Tennessee 4-0 for first time ever PANTHERS 24, FALCONS 9: Smith honors Lucas after TD JAGUARS 30, TEXANS 27, OT: Scobey kicks game winner SAINTS 31, 49ERS 17: McAlister scores first TD of year

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