In a New Republic interview, first fan Barack Obama said he'd think long and hard before letting a son of his play tackle football. Former Dallas Cowboys quarterback and Fox Sports anchor Troy Aikman last year publicly wondered about the long-term viability of the NFL: "At some point, football is not going to be the No. 1 sport." And Baltimore Ravens safety Bernard Pollard told CBSSports.com that he would not be surprised to see the first player killed during an NFL game, noting that he doesn't think the sport will exist in its current form in 30 years.

All the doomsaying comes as the country's most-popular and -successful sports league has never been healthier. The league generated $9.5 billion in revenue in 2012 vs. $7.5 billion for Major League Baseball. Super Bowl XLVI was the most-watched TV show in history, averaging 111.3 million viewers. NFL game telecasts accounted for 31 of the 32 most-watched programs this past fall.

As was proved just yesterday, the Super Bowl is the ultimate advertising showcase, pulling in nearly $4 million for 30-second spots this year. National advertisers spent $3.3 billion on pro football in 2011, according to Nielsen, dwarfing the $975 million spent on college football.

But there are troubling trends that threaten to dent, if not crack, the NFL's "shield" brand in the future.

Although some 3 million kids play organized tackle football, according to USA Football, the number of kids ages 6- to 12-years-old participating regularly has been dropping around 5% annually for the past three to four years, said Tom Cove, president of the Sports & Fitness Industry Association. And as more parents steer their kids away from tackle football because of concern over concussions, it raises the potential of fewer high school and college players -- and a "smaller talent pool" for the NFL, said Dan Wetzel, national columnist for Yahoo Sports.

While the future is cause for concern, the past is haunting the league as well. More than 1,500 ex-players are suing the NFL in federal court, claiming the league fraudulently concealed the risk of brain trauma caused by playing pro football.

Add to that a slight decline in popularity for football. The percentage of respondents who named the NFL their favorite sport dropped to 34% from 36% in 2012 in the latest Harris Poll this January. The statistic didn't escape NFL Commissioner Roger Goodell, who likes to remind complacent staffers that boxing and horse racing were once among the country's favorite sports. During a meeting with 32 team owners in March, he ticked off the names of other corporate giants that are either defunct or no longer leaders: Blockbuster, Enron, Pan Am, Bethlehem Steel, General Foods and E.F Hutton.

His NFL defense? An offense. It's trying to counter negative coverage with advertising and PR campaigns designed to position the league as positive, proactive and transparent about its key issues.

Last week the NFL was putting the finishing touches on a branding spot by Grey Advertising slated to air during yesterday's Super Bowl and it is planning a TV spot promoting the NFL Network and a couple of 10-second quick hitters "celebrating the game of football," said league spokesman Brian McCarthy.

The feel-good ad strategy about the bright future of pro football builds on the NFL's "Evolution" Super Bowl spot from last year, in which Baltimore Ravens middle linebacker Ray Lewis glowingly described the helmet, equipment and rules changes that have made the game safer than ever before.

"We certainly have come a long way. Thing is, we're just getting started," narrates Mr. Lewis as viewers see the game change from the leather helmets of the early 1900s to the face masks and hard-plastic helmets of today's NFL. "Here's to making the next century safer and more exciting than ever. Forever forward. Forever football."

The league also launched a website at NFLEvolution.com that focuses on health and safety issues. Last week, the site featured player responses to President Obama saying it would be a tough call to let his son play tackle football. And the NFL Players Association is making a $100 million grant to Harvard for concussion studies, along with $30 million to National Institutes of Health for brain research. It's also sponsoring studies of new helmet designs. The NFL is not working with a crisis-PR agency or adviser, Mr. McCarthy said.

It's a start, but the NFL still faces an inherent marketing challenge. Nobody knows that better than the players. "The NFL is going to do what it can to make the game safe—but it's never going to be a "safe' game," Justin Tuck, a two-time Super Bowl winner with the New York Giants, told Ad Age. "It's a violent game. That's what draws fans all over the world to watch it. Society is drawn to the violence. The bigger the hits, the louder the crowd cheers."