By KEVIN KERNAN

I wonder what Wellington Mara would think about all this as the Giants head into a pivotal game against one of Mara’s favorite coaches, Bill Parcells Sunday?

Actually, I really don’t have to wonder. I knew him too well. Mr. Mara would not be happy. He could put up with losing, even though he didn’t like it, but he wouldn’t put up with the bickering between the Giants and the ridiculous accusations by Michael Strahan and other Giants that the media is at fault here.

Here’s what’s really wrong with the Giants.

There is a lack of leadership across the board and once Tiki Barber made it clear that the Tom Coughlin’s game plans were weak, the Giants began to weaken as a unit.

There is only one way to stop the collapse. It is so obvious. Every Giant fan recognizes the problem.

Until Eli Manning starts acting like a quarterback, in team meetings, in the huddle and on the field, the Giants will continue to blow fourth quarter leads and games.

Everyone likes to think that a head coach runs a football team, and those coaches do, until the game starts. Once the ball is kicked off, that game belongs to the quarterback.

The QB sets the tone by his actions, his performance and his words. There has to be strength of character, there has to be a sense that the teammates believe in the quarterback no matter what kind of day that quarterback is having.

Yes, Plaxico Burress quit on that game-changing interception in last week’s terrible 24-21 loss to the Titans, but you could see from his body language that he quit on Manning at that point because it was such a poor pass. Just one of many poor passes thrown by Manning in key situations.

It is inconceivable to me how Manning so often throws off the wrong foot. He does not sense where the rush is coming from, does not step up at the right time in the pocket and all that results in horrible throws. Time and again.

In his last four games, Eli has thrown seven interceptions and only three touchdown passes. That is pathetic.

The final interception Sunday was one of the worst in Giants history. They had already given away a 21-point lead and now Manning gave the game away with that pass to nowhere that wound up in the hands of the acrobatic Pacman Jones.

Manning will go down in history as only the third quarterback to ever be on the losing side of a 21-point lead with less than 10 minutes to go in the game.

Until Eli Manning grows up, the Giants are going nowhere.

Blame Coughlin, blame that reporter from ESPN as Strahan did, blame Burress for quitting on the pass, but the Giants collapse is Manning’s fault.

Until he gets in the face of his teammates when they quit on a pass things will not change. Would Phil Simms allow his receivers to quit on a pass and not get in their face? Simms would have been all over Burress.

Right now Manning looks like a quarterback who has been spoon-fed success his entire life, not a quarterback who has had to fight for his position, for his job.

He’s always had the advantage of being Archie’s kid and Peyton’s younger brother and he has the talent and the name, but he has yet to show the guts needed to be a championship quarterback.

The good thing is that young Eli can learn from all this. Simms made plenty of mistakes when he was young and I remember covering most of them, but eventually Simms stopped making critical mistakes because he was tough enough to fight back.

Eli Manning has not shown that kind of toughness.

If Mr. Mara were around today, I could see him having a nice little chat with his young quarterback. In a gracious, grandfatherly way he would tell Eli, “Time to toughen up, son.’’

Starting Sunday against the Cowboys.