FOXBORO -- Training camp may be the time when NFL coaches seek answers to the questions that arise from the end of one season to the start of the next, but not all questions are answered before the season starts.

As many coaches, including the Patriots' Bill Belichick, are fond of saying, `` the season is a marathon, not a sprint.'' Even with only 16 games as opposed to 10 times than number in baseball, the development of a football team doesn't begin in July and end in early September.

It's an ongoing process, requiring adjustments and planning for eventualities that may or may not arise. How well a team adjusts to adversity dictates its success -- as the Patriots displayed in 2001, 2003 and 2004, when injuries to key players did not derail trips to pro football's championship game.

The Patriots' defensive unit has undergone significant (if not sweeping) change since the final gun of Super Bowl XXXIX. Training camp, which begins at 8:45 this morning at Gillette Stadium, will answer some of the questions posed by those changes, but how well Belichick and his staff have adapted to them won't be fully apparent until well into the season.

But the work begins in earnest today, so here are five of the most pressing questions about the 2005 Patriots' defense (and one bonus question) that are being pondered as the two-time defending world's champions convene at Gillette Stadium: 1. Can the Patriots replace Tedy Bruschi?

If nothing else has been obvious over Bill Belichick's five previous seasons as the Patriots' head coach, it's that any player can be replaced. Just ask Drew Bledsoe and Lawyer Milloy.

But the circumstances of Bruschi's departure from the field are profoundly different than those that moved the `` franchise'' quarterback and fiery safety elsewhere. Those were performance issues. Other players who left of their own volition, such as former Pro Bowl center Damien Woody or nose tackle Ted Washington, were quickly replaced through the hard work of the personnel department headed by Scott Pioli.

Bruschi's departure was unexpected and tragic -- a player at the top of his game whose life and well-being were suddenly threatened by a stroke. The veteran linebacker from Arizona returned quickly to physical activity, but he made the wise decision to sit out the 2005 season to continue his rehabilitation, all toward the goal of eventually determining whether a resumption of his career is possible, or whether his family concerns will outweigh the burning desire to play again.

Almost from the moment Bruschi was taken to the hospital, the personnel department began the search for linebackers who might have to replace him -- a search that may have been undertaken anyway, given the advancing age of the linebacking corps in general.

On paper, that mission appears to have been accomplished through the signings of accomplished veteran Chad Brown (late of Seattle and Pittsburgh) and promising ex-Chief Monty Beisel. Ryan Claridge, the rookie from UNLV, may also be an important factor before the season's out.

But it will be extremely difficult to `` replace'' the intangibles that Bruschi brought to the field, particularly his fiery leadership and penchant for making the big play when it was most needed in the context of a game. There are plenty of `` leaders'' on the Patriots' defense, but Bruschi was the personification of the team's work ethic.

His illness was quite sobering to everyone surrounding the Patriots, from the starters all the way down to the parking lot attendants. But that sort of circumstance often produces an iron-willed resolve among players who have any sort of personal and professional pride -- especially these Patriots, who are used to overcoming significant odds against them.

With Bruschi present in the locker room, weight room and meeting rooms, the other linebackers will be reminded daily of what they have lost, and what they need to replace. Players such as Willie McGinest, Mike Vrabel and Rosevelt Colvin (who knows what it means to beat overwhelming odds against him following hip surgery) will undoubtedly step up their play and their leadership in honor of their fallen teammate.

Another fly fell into the ointment Thursday when inside linebacker Ted Johnson, 32, announced his retirement after 10 seasons because of the cumulative effects of several concussions. His unexpected absence will force Brown and Beisel into larger roles than originally anticipated, and could force Vrabel to move to inside linebacker. 2. How badly will the defense miss former coordinator Romeo Crennel?

Badly -- perhaps even more than the offense will miss ex-coordinator Charlie Weis.

Crennel, the new head coach of the Cleveland Browns, may have been the most underrated member of the Patriots' braintrust, at least by those with only a cursory knowledge of the team. He never received full credit publicly for his contributions to the Patriots' defensive game-planning, probably because Belichick is regarded as a defensive genius, Therefore, it was assumed by some in the national media that the strategies employed to stop opponents were devised by Belichick with Crennel a mere puppet in the play-calling process.

Not so. The game plans may have been concepts provided first by Belichick, but the specifics were ironed out jointly by the head coach and his assistants, and Crennel was the fine-tuner who made sure the concepts could and would work in real-life application.

Crennel was also the `` yin'' to Weis' `` yang'' on the Patriots' coaching staff. While the offense may have needed Weis' bluster and intensity, Crennel offered stern but soothing guidance to players who are already more intensely motivated, given the attacking nature of today's defenses.

Eric Mangini, although young and inexperienced as a coordinator, has the mentality of a teacher and instructor and has had a lot of input into game-planning, so the defense should be in good hands. But with Belichick expected to be more involved in the offensive game-planning because he didn't name a true coordinator on that side of the ball, Crennel's departure will still be keenly felt.

3. Is the secondary ready for life without Ty Law?

That's assuming, of course, that the multi-time Pro Bowl cornerback (still recuperating from last year's broken foot) does not return at a reduced salary. But given that the vultures have already struck and safety Dexter Reid appropriated Law's No. 24, that doesn't appear likely.

The answer? The secondary has no choice. But it should also be immediately remembered that the Patriots won a third Super Bowl championship last year with both of their season-opening cornerbacks, Law and Tyrone Poole, out of action due to injuries.

Poole is back, but there's no guarantee he will reclaim his starting job. The Patriots added veterans Duane Starks and Chad Scott through free agency, a total of 17 years of experience among them, and they will join Poole, Asante Samuel, 2004 breakthrough rookie Randall Gay and rookie Ellis Hobbs in the effort to give the Patriots solid, consistent play at the corners.

They'll miss Law's talent, but considering his foot injury and longevity, there's no guarantee Law would have been the Law of olde had he returned.

At safety, the Patriots have a solid duo in Rodney Harrison and Eugene Wilson. But Harrison is reportedly unhappy with his contract and is getting up there in years -- although he showed no signs of degradation last season -- so depth must come from Reid, veteran Antuan Edwards and Guss Scott, a promising rookie last year who was lost to a preseason injury.

4. What in the world is Richard Seymour thinking?

That's a good question. If he didn't show up at camp this morning, it's because he doesn't believe that talks between his agent and the Patriots on a contract extension are moving in the direction he'd like.

The Patriots usually stick to their guns when a player wants more money with two years left on his original pact, but Seymour -- a three-time Pro Bowl selection at defensive end -- may have enough cache to earn the same nod that Tom Brady got when it comes to sweetening the pot.

Reportedly, Seymour does not want to be a distraction. That's good, but he should also remember that the Patriots have an uncanny ability to put anyone on the field and still win. He didn't play in two playoff games last year and the Patriots still got to another Super Bowl, so it doesn't pay to make threats with a BB gun when the opposition has nuclear weapons.

The defensive line is deep and talented. From among Ty Warren, Jarvis Green, Vince Wilfork, Rodney Bailey and Marquise Hill, the Patriots may already have enough to survive the loss of an accepted superstar with only a modicum of decline. But both sides know that the Patriots are better with Seymour than without him both on and off the field.

5. Who'll be the toughest opponent to stop on this year's schedule?

Some might vote for the Atlanta Falcons (Aug. 9 at the Georgia Dome) because of the ever-elusive Michael Vick, but the Patriots always seem to find the one vulnerability in an accepted superstar's game and attack it relentlessly. They've faced Vick before and contained his scrambling well enough to make him rely more upon his supporting cast, which remains questionable.

The bet here is that the Miami Dolphins (Nov. 13 at Miami, Jan. 1 at Gillette), under former Belichick protege Nick Saban, will have progressed enough both offensively and defensively in Saban's system by the time the teams meet to give Belichick and his reconstituted coaching staff fits. This may be when the former coordinators will be missed the most.

Bonus question: Can the Patriots become the first team in NFL history to win three straight Super Bowls?

Tell the truth. Back in 1990, in the midst of the Rod Rust fiasco, or at the end of the 1993 season, when the Patriots were a heartbeat from being moved to St. Louis, did any of you dream that it was even remotely possible that `` New England Patriots'' and `` dynasty'' could be used in the same sentence without it being a joke?

Anything is possible.

As usual, injuries will play a huge role in the fortunes of all NFL teams over the course of a 17-week regular season. But if key Patriots stay healthy and productive and a few nagging gaps are filled (especially at inside linebacker), there's no reason why they shouldn't be in the hunt for another trip to the Big Game.

The schedule-makers didn't help, putting the Patriots on the road for four of the first six weeks, or throwing six playoff teams from last year at them in the first nine weeks. If they can get through those stretches with their helmets on straight, fans might want to start packing their cold-weather gear for a trip to Detroit.

MARK FARINELLA may be reached at 508-236-0315 or via e-mail at mfarinel@thesunchronicle.com