ATLANTIC CITY, N.J. >> America’s gambling industry predicts $10 billion will be bet on the March Madness college basketball tournament — nearly all of it illegally or off-the-books.

That’s one of the reasons the American Gaming Association favors the full legalization and regulation of sports betting in the United States.

The U.S. Supreme Court is weeks away from ruling on New Jersey’s challenge to a law limiting legal sports betting to just four states: Delaware, Montana, Nevada and Oregon, and a ruling that legalizes sports betting nationwide could provide new revenue opportunities for cash-strapped state governments, as well as casino companies.

The group found 54 million people — or about a quarter of the U.S. adult population — participated in a sports betting pool last year, spending $18 billion on entry fees. That includes 24 million who filled out basketball brackets pools and spent $2.6 billion on entry fees.

It also conducted a survey that found that roughly two-thirds of U.S. states make it illegal to participate in sports betting pools if money is involved. Enforcing those laws, however, has not been a priority for law enforcement.

“Our current sports betting laws are so out of touch with reality that we’re turning tens of millions of Americans into criminals for the simple act of enjoying college basketball,” said Geoff Freeman, president and CEO of the American Gaming Association. “The failed federal ban on sports betting has created an illegal, unregulated sports betting market that offers zero consumer protections and generates zero revenue for state and tribal governments.”

Freeman said only 3 percent of the $10 billion the group predicts will be wagered on the games will be done through legal Nevada sports books, or about $300 million.

The group also counted 48 pieces of sports betting legislation active in 18 state legislatures across the country as lawmakers anticipate a favorable Supreme Court ruling and prepare for the advent of legal sports betting.

Freeman predicted “a flood of new products” if sports betting is legalized, including increased opportunities for bets on events within a game and not just on its final score or statistics.

“There’s a lot of money that’s going to go to innovation that’s currently sitting on the sidelines,” he said.

The Council on Compulsive Gambling of New Jersey says “sports betting is a cause for concern.” While neutral on gambling, the group has been contacting New Jersey lawmakers to discuss needs that will arise if sports betting is legalized.

“Sports betting may have more appeal to our children, it has the potential to affect the integrity of the games, and it may put many more people at risk for problem and disordered gambling,” said Neva Pryor, the group’s executive director.