The Supreme Court ruled Monday that cities and states must abide by the 2nd Amendment, strengthening the rights of gun owners and opening a new chapter in the national debate over gun control.

In a 5-4 decision, the justices said the right to have a handgun for self-defense is "fundamental from an American perspective (and) applies equally to the federal government and the states."

The high court overturned 19th Century rulings that said the 2nd Amendment restricted only federal gun laws, not local or state measures. The decision will almost certainly void ordinances in Chicago and Oak Park, Illinois which forbid residents from having a handgun at home. The justices ruled in favor of the Chicago residents who wish to have a gun and sent the case back to Chicago for a lower court to issue a final ruling.

By extending the reach of the 2nd Amendment, Monday's ruling opens the courthouse doors nationwide for gun-rights advocates to argue that that restrictions on firearms are unconstitutional.

Legal experts on both sides of the gun-control debate predicted the ruling will trigger more lawsuits. They disagreed, however, whether it will lead to gun laws being struck down, beyond a city's total ban on handguns.

"This case is only the beginning of the debate. Gun-ownership rights—like free-speech rights--are not absolute, and state and local governments retain the authority to enact reasonable gun-control laws," said Rick Garnett, a law professor at Notre Dame University.

Typically, residents can have a rifle or shot gun in any state without a permit. The main exceptions are for persons with a felony record or who are mentally ill, and the Supreme Court has already said those "reasonable regulations" can stand.

Seven states, including California, forbid assault weapons or semi-automatic weapons, the court noted. Those restrictions will face a legal challenge, gun rights advocates said.

The National Rifle Association also said it plans to focus on how some laws are enforced. For example, California authorizes residents to carry a concealed weapon in public with a permit. But NRA lawyers say that sheriff's offices in Los Angeles and San Francisco rarely issue a permit, and they want to sue to challenge that practice.

"You will see lots of lawsuits, but the vast majority of laws are likely to be upheld," said UCLA Law Professor Adam Winkler, an expert on the 2nd Amendment. "The only thing we know for sure is that it's unconstitutional to prohibit possession of a hand gun at home."

Though the high court split along ideological lines, the ruling won bipartisan praise in Washington, where Democrats have increasingly shied away from advocating gun control. Senate Majority Leader Harry Reid (NV) and Judiciary Committee Chairman Patrick Leahy (Vt.) joined Republicans in support of the outcome. For their part, the justices are deeply split on both the meaning of the 2nd Amendment and wisdom of gun-control measures. Justice Samuel A. Alito Jr. said crime data from the Chicago Police Department "reveal that the city's handgun murder rate has actually increased since the ban was enacted and that Chicago residents now face one of the highest murder rates in the country."

In dissent, Justice Stephen G. Breyer said firearms "cause well over 60,000 deaths and injuries in the United States each year. Gun regulation may save lives. Some experts have calculated, for example, that Chicago's hand-gun ban has saved several hundred lives, perhaps close to 1,000, since it was enacted in 1983."

Two years ago, in a case from Washington, DC, the court for the first time declared that the 2nd Amendment protects the gun-rights of individuals. But the District is a federal city and not a state, and the earlier ruling did not make clear whether state laws or city ordinances were affected.

In McDonald v. Chicago Monday Alito explained that in the 20th Century, the Bill of Rights was extended to apply to states and cities. There is no reason to leave out the 2nd Amendment, he said. Chief Justice John G. Roberts Jr. and Justices Antonin Scalia, Anthony M. Kennedy and Clarence Thomas joined to form the majority.

Alito repeated the court's earlier assurance that "reasonable regulations" of firearms can stand. "Despite the doomsday predictions" (of the city's lawyers), extending the 2nd Amendment "does not imperil every law regulating firearms."

The dissenters said they feared the ruling will have a severe and dangerous impact across the country. On his final day as a justice, John Paul Stevens said he continued to believe the 2nd Amendment was "adopted to protect the states from federal encroachment," not to undercut their gun laws. Justice Ruth Bader Ginsburg and Sonia Sotomayor joined Breyer's even longer dissent.

The court did not explain why it stopped short of striking the Chicago ordinance. But in the past two years, a federal judge and the U.S. court of appeals said that high court precedents barred them from striking down the Chicago ordinance. Now that those precedents have been set aside, the high court may have thought the judges in Chicago deserved the chance to rule directly on the constitutionality of Chicago's hand gun ban.

Outside the court, National Rifle Association of America CEO Wayne LaPierre said it was a "monumental day." He said the NRA "will not declare victory until any law abiding citizen can go out, buy a firearm, own a firearm, protect themselves with it and use it for any other lawful purpose."

But Paul Helmke, president of the Brady Campaign to Prevent Gun Violence, told reporters the ruling was not a surprise and set a "very narrow" definition of protected gun rights.

Alan Gura, the lawyer for lead plaintiff Otis McDonald, said "people very, very soon in Chicago will be able to buy and lawfully possess handguns."

David.Savage@latimes.com

Katherine Skiba,Jennifer Martinez and Julia Love contributed to this article.