New York City, which has some of the most restrictive and perhaps even unconstitutional gun laws in the nation, will become a flash point in the legal battle over gun control, as civil rights proponents turn their attention to enforcing the historic gun rights decision issued yesterday by the Supreme Court.

For the first time in the nation’s history, the Supreme Court has recognized that the Second Amendment affords individuals the right to keep a gun at home for protection.

“The movement to end private firearms ownership in America is over,” the gun rights attorney who argued the case before the federal high court, Alan Gura, told The New York Sun.

Yesterday’s 5-4 ruling, which declared a Washington, D.C., handgun ban to be unconstitutional, will put advocates of municipal gun control on the defensive. Gun proponents say to expect new suits challenging handgun bans and licensing restrictions from New York to Chicago to San Francisco.

That a case on gun ownership was decided by just a single vote will serve to thrust the issue of future Supreme Court appointments to the fore of the presidential race. Two of the justices in yesterday’s majority — justices Kennedy and Scalia — are older than 70, raising the question of whether five justices in favor of gun rights will sit on the court in the coming years.

While Senator Obama, the presumptive Democratic nominee for the presidency, issued a tepid response in praise of the ruling yesterday, he appeared to defend the handgun ban in effect in his home city. He said he “believed that the Second Amendment protects the right of individuals to bear arms.”

Mr. Obama opposed the confirmation of two of the justices who formed yesterday’s majority, Chief Justice Roberts and Justice Alito.

Senator McCain, the presumptive Republican nominee, voted to confirm in each instance. He issued a more enthusiastic statement calling the decision a “landmark victory,” and praising the Supreme Court for recognizing that “gun ownership is a fundamental right — sacred, just as the right to free speech and assembly.”

The immediate effect of yesterday’s decision, legal experts say, will be to unleash numerous gun cases before the federal courts, as challenges are brought to establish what, if any, gun rights belong to nonviolent felons, illegal immigrants, and those convicted of misdemeanor domestic abuse.

Gun ownership is widespread in this country, with about 300 million firearms in the hands of some 57 million Americans, according to a 2004 Harvard University survey.

Yet the Supreme Court’s past sporadic pronouncements on the Second Amendment — it last heard a case on the amendment in 1939 — had left many uncertain until yesterday that private gun ownership is indeed protected under the Constitution. The sticking point has always been whether the Second Amendment, which states, “A well-regulated militia being necessary to the security of a free State, the right of the people to keep and bear arms shall not be infringed,” protected only the power of states to form militias or whether it granted individual persons, regardless of military service, the right to keep a gun.

Writing for the majority, Justice Scalia found that the Second Amendment guarantees that guns are available to help citizens exercise their broad and basic right for self-protection. In focusing on the right to self-defense, Justice Scalia gave short attention to other arguments used by gun-rights advocates such as the importance of training citizens for military service or the right to resist a government that turns tyrannical.

The Second Amendment, Justice Scalia wrote, “surely elevates above all other interests the right of law-abiding, responsible citizens to use arms in defense of hearth and home.”

Nor was it enough for Washington to only allow citizens to own long guns, such as rifles and shotguns.

“The American people have considered the handgun to be the quintessential self-defense weapon,” Justice Scalia wrote.

Because none of the other four justices in the majority — Justices Kennedy, Thomas, Alito, or the chief justice — wrote a concurring opinion, it is impossible to tell how far each member of the five would be willing to go in favor of gun rights. But the opinion that emerged shows some signs of ambivalence about whether an armed populace is necessarily good social policy.

“Undoubtedly some think that the Second Amendment is outmoded in a society where our standing army is the pride of our Nation, where well-trained police forces provide personal security, and where gun violence is a serious problem,” Justice Scalia wrote for the majority. “That is perhaps debatable, but what is not debatable is that it is not the role of this Court to pronounce the Second Amendment extinct.”

The majority also went to lengths to argue that their ruling would not have the effect of overturning all gun control laws.

“Like most rights, the right secured by the Second Amendment is not unlimited,” Justice Scalia wrote, adding that ownership of military-type rifles was not likely to receive protection under the Second Amendment.

“Nothing in our opinion should be taken to cast doubt on longstanding prohibitions on the possession of firearms by felons and the mentally ill, or laws forbidding the carrying of firearms in sensitive places such as schools and government buildings, or laws imposing conditions and qualifications on the commercial sale of arms,” Justice Scalia wrote.

In a dissent, Justice Stevens warned that the court was undermining much of existing gun control, even opening the way for felons, whom federal law currently bans from possessing firearms, to assert a right to gun ownership.

“I fear that the District’s policy choice may well be just the first of an unknown number of dominoes to be knocked off the table,” Justice Stevens wrote.

In arguing that the Second Amendment did not grant a right to gun ownership unconnected from military service, Justice Stevens said that majority opinion was the equivalent of an “announcement of a new constitutional right.”

“Until today, it has been understood that legislatures may regulate the civilian use and misuse of firearms so long as they do not interfere with the preservation of a well-regulated militia,” Justice Stevens wrote.

Justices Ginsburg, Souter, and Breyer all joined the dissent, with Justice Breyer writing separately as well.

Washington’s handgun ban was considered the most restrictive in the nation, with Chicago’s ban a close second.

In New York, handguns are permitted, but the licensing process is expensive and lengthy. Handgun owners must pay a fee of more than $1,200 a decade. Getting a license can take more than six months. Those obstacles violate a constitutional right to keep a firearm, gun rights lawyers say, though the city has said it thinks the laws pass constitutional muster.

The majority’s decision did not directly say that the Second Amendment will apply to limit states and local municipalities from enforcing handgun bans or burdensome licensing restrictions. Yesterday’s case, because it dealt with a Washington law, only established that the Second Amendment limits the types of gun regulation the federal government can enact.