By DAVE GOLDBERGAP Football Writer

New England begins its quest for an unprecedented third straight Super Bowl victory and fourth in five years without the two coordinators who helped Bill Belichick win the first three titles.

And that quest also will take place without linebacker Tedy Bruschi, the heart of the defense, who is sitting out the season after suffering a mild stroke.

Philadelphia goes to camp with Terrell Owens, the catalyst in its run to the Super Bowl, threatening to hold out just a year after arriving and signing a big contract.

As NFL camps open over the next few days, New England and Philadelphia start as favorites to meet again in the Super Bowl. But this is an era of uncertainty, and even two teams that have been the NFL’s most consistent in the last four years have their problems.

‘‘Each year is its own entity,’’ says Bill Belichick, who has put himself in a class with — dare we say it — Vince Lombardi with his success in New England the past four years.

‘‘There are new people and there are changes every year. You have to build and rebuild your team. Every team in the league is going through the same thing. We are part of it. It’s unique.’’

That’s why 31 other teams are opening camp with hopes of succeeding the Patriots as champion.

Well, not quite 31 — not San Francisco, Cleveland or Miami, which are starting over. Not Tennessee, which purged a half-dozen veterans from a highly successful run from 1999-2004. And not a half-dozen or more teams that just don’t have the players, including Washington, where Dan ‘‘The Fan’’ Snyder has made a mess of things since buying the team in 1999.