With a key provision of Maryland’s gun-control laws hanging in the balance, a federal appeals court on Wednesday wrestled with the broad question of whether the individual right to keep a firearm in one’s home for self-defense extends beyond the front door.

The lawsuit, one of many challenging gun restrictions throughout the country, seeks to make it easier for residents to carry handguns in public places.

If the U.S. Court of Appeals for the 4th Circuit upholds a lower court decision, state police in Maryland anticipate that thousands of additional residents could legally carry a loaded firearm.

In the four years since the Supreme Court used a D.C. case to declare that the Second Amendment guarantees a person’s right to own a firearm, lower courts have been left to consider whether that right applies to such public spaces as shopping malls and city streets.

At issue in Maryland is the state’s requirement that applicants provide a “good and substantial reason” to the state police to obtain a permit for carrying a handgun.

“If you have a right to do something, you don’t need to prove you’re entitled to it,” said attorney Alan Gura, who argued the case Wednesday on behalf of a Navy veteran, Raymond Woollard, and the Second Amendment Foundation. “The need for self-defense frequently arises outside the home.”

Woollard was initially granted a handgun permit after his son-in-law broke into his house in Baltimore County in 2002 and demanded car keys so he could go out and buy drugs. Woollard aimed his gun at his son-in-law, who then tackled Woollard before he could be subdued by Woollard’s son, who also pointed a gun at him.

Woollard’s renewal request was denied in 2009, however, when a state board ruled that he had not shown a “good and substantial reason to wear, carry or transport a handgun as a reasonable precaution against apprehended danger.”

A federal judge in Baltimore sided with Woollard in March. U.S. District Judge Benson Everett Legg wrote that “the right to bear arms is not limited to the home” and that Maryland’s handgun permit system is essentially a “rationing system.”

In defending the state’s system, attorneys for the government argued in their brief that the provision “was enacted with the express purpose of reducing handgun violence in public places.”

Gun-control advocates and Maryland law enforcement officials warn in court papers that putting more firearms on the street would make the job of police officers more dangerous and could lead to more violence in everyday conflicts.

Since the 1970s, Maryland law has left it to law enforcement to decide whether a person should be allowed to carry a handgun. There are about 12,700 permits statewide, primarily issued to people such as armored car drivers, security guards and prosecutors. Permits are also issued for “personal protection” if a threat can be verified, something gun-rights advocates say is very difficult to prove.

If the “good and substantial” requirement is eliminated, state police estimate a wave of 15,000 new applicants within a 12-month period. Legislative analysts have predicted a much smaller increase of about 3,600.

Maryland’s current practice is similar to licensing systems in California, New York and New Jersey — all states facing similar legal challenges. In the District, Gura is leading another pending case to make it legal to carry a loaded firearm in the nation’s capital.

In “shall issue” states such as Virginia and Florida, the default position is for law enforcement to issue a permit unless the applicant falls under a list of specific restrictions.

At the 4th Circuit in Richmond on Wednesday, members of a three-judge panel pressed Gura about the limits of his argument. Judge Andre M. Davis asked whether the state could permit the open carrying of a handgun but not a semiautomatic weapon.

When Gura did not immediately answer, Davis said, “I still haven’t heard yes or no.”

Gura responded, “Probably not.”

Later, Judge Robert B. King noted that Maryland’s law does not require a permit to carry a shotgun in public and that the General Assembly specifically addressed handguns because they “were used a lot by criminals on the street.”

Gura responded that “handguns are also indisputably the weapon of choice for law-abiding citizens” and that “nobody carries a shotgun around to defend themselves.”

Assistant Attorney General Matthew Fader, who argued the government’s case, noted that Maryland does not require a permit to keep a firearm in one’s home and allows residents to carry a handgun “if you have a demonstrable need for self defense.”

But Judge Albert Diaz sounded skeptical, noting that the law “places the burden on the people” to provide a justification to police.

Regardless of the outcome, one of the parties in the case will likely petition the Supreme Court, something Davis alluded to near the end of the session.

“I suppose if we wanted to do everyone a favor,” he said, “we would just . . . send this to the Supreme Court and get a clear answer for a change.”