In a major victory for gun rights activists, a federal appeals court ruled Thursday that concealed firearms regulations in California violate a Second Amendment right to bear arms in public for self-defense.

The opinion is likely to spark renewed debate over gun control measures in a country plagued by spontaneous shootings at schools and other public places. And it sets the stage for a potential Second Amendment showdown at the US Supreme Court.

The 2-to-1 decision came in a case challenging a San Diego County gun regulation that required residents to prove they have a justifiable need to carry a concealed weapon.

Unless the applicant could demonstrate a heightened risk to his or her safety, the permit would be denied.

The majority judges said such a requirement cannot be imposed on a constitutional right. Responsible, law-abiding citizens do not have to justify whether they are under an imminent threat to their safety to carry a gun for protection, the judges said.

The Second Amendment guarantees to them the authority to decide for themselves whether to carry a weapon for personal safety. At issue was whether gun control regulations in California and San Diego prevented citizens from exercising their Second Amendment rights.

“The question is not whether the California scheme (in light of San Diego County’s policy) allows some people to bear arms outside the home in some places at some times; instead, the question is whether it allows the typical responsible, law-abiding citizen to bear arms in public for the lawful purpose of self-defense,” wrote Appeals Court Judge Diarmuid O’Scannlain for the two-judge majority.

“To be clear, we are not holding that the Second Amendment requires the states to permit concealed carry,” Judge O’Scannlain said. “But the Second Amendment does require that the states permit some form of carry for self-defense outside the home.”

California law prohibits all gun owners from openly carrying firearms. So the only means of exercising a right to bear arms for personal protection in California would be to obtain a concealed carry permit.

Gun owners challenged the San Diego permit process in federal court, arguing that they should not have to prove they face an imminent threat to their safety to qualify for a concealed carry permit.

County officials defended the concealed carry permit regime, arguing that the Supreme Court in its landmark gun rights decision in 2008 said concealed carry restrictions were “presumptively lawful.”

The high court observed that the majority of 19th-century courts that examined the issue concluded that prohibitions on concealed weapons did not violate the Second Amendment, lawyers for the county argued.

Judge O’Scannlain brushed the point aside. He said the California/San Diego regulations failed because they left gun owners with no choice between open carry – which is illegal in California – and concealed carry, which is subject to the discretion of government officials.

“California’s favoring concealed carry over open carry does not offend the Constitution, so long as it allows one of the two,” the judge wrote.

In a dissent, Judge Sidney Thomas said the county’s policy was constitutional and fully in line with the Supreme Court’s observation that such regulations are “presumptively lawful.”

Judge Thomas said the appeals court should have focused on that narrow question. “There is no need to reach any other issue,” he said. “In dealing a needless, sweeping judicial blow to the public safety discretion invested in local law enforcement officers and to California’s carefully constructed firearm regulatory scheme, the majority opinion conflicts with Supreme Court authority, the decisions of our sister circuits, and our own circuit precedent.”

To date, four other appeals courts have examined the issue of whether the Second Amendment protects a citizen’s right to bear arms outside the home for self-defense.

Three courts have upheld gun regulations, one found a broad constitutional right. Thursday’s decision makes the split among the appeals courts 3 to 2, a substantive disagreement that increases the likelihood that the Supreme Court will examine the issue.

O’Scannlain knew his decision would spark controversy.

“We are well aware that, in the judgment of many governments, the safest sort of firearm-carrying regime is one which restricts the privilege to law enforcement with only narrow exceptions,” he wrote.

The judge then quoted from two recent Supreme Court decisions: “Undoubtedly some think that the Second Amendment is outmoded in a society where our standing army is the pride of the Nation, where well-trained police forces provide personal security, and where gun violence is a serious problem. That is perhaps debatable, but what is not debatable is that it is not the role of this Court [or ours] to pronounce the Second Amendment extinct.”

O’Scannlain added: “Nor may we relegate the bearing of arms to a second-class right, subject to an entirely different body of rules than other Bill of Rights guarantees.”

The case is Peruta v. County of San Diego (10-56971).