In a 2 to 1 decision in March, a panel of judges for the U.S. Court of Appeals for the D.C. Circuit ruled that the city's prohibition against residents keeping handguns in their homes is unconstitutional. In May, the full appeals court declined a petition from the city to reconsider the panel's decision.

Some gun control advocates have cautioned that a defeat in the Supreme Court could lead to tough gun laws being overturned in major cities, including New York, Chicago and Detroit. Fenty said the District had no choice but to fight because more guns in homes could lead to increases in violent crime and deadly accidents.

"The handgun ban has saved many lives and will continue to do so if it remains in effect," Fenty said. "Wherever I go, the response from the residents is, 'Mayor Fenty, you've got to fight this all the way to the Supreme Court.' "

Gun rights advocates welcomed the chance to take the fight to the high court. A central question the D.C. case poses is whether the Second Amendment protects an individual's rights to keep and bear arms.

Experts say gun rights advocates have never had a better chance for a major Second Amendment victory, because a significant number of justices on the Supreme Court have indicated a preference for the individual-rights interpretation.

"Any accurate, unbiased reading of American history is going to come down to this being an individual right," said Wayne LaPierre, executive vice president of the National Rifle Association. "To deny people the right to own a firearm in their home for personal protection is simply out of step with the Constitution."

The city's three-decade-old gun ban was challenged by six D.C. residents -- backed by the libertarian Cato Institute -- who said they wanted to keep guns in their homes for self-defense. The District's law bars all handguns unless they were registered before 1976; it was passed that year to try to curb gun violence, but it has come under attack in Congress and in the courts.

The Second Amendment 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."

The last Supreme Court ruling on the issue, in Miller v. the United States, is considered by many to define the right to bear arms as being given to militias, not to individuals.

U.S. District Judge Emmet G. Sullivan dismissed the residents' lawsuit -- Parker v. the District of Columbia-- several years ago, ruling that the amendment was tailored to membership in a militia.

But the appeals panel ruled in March that the District has a right to regulate and require registration of firearms but not to ban them in homes. The ruling also struck down a section of the law that required owners of registered guns, including shotguns, to disassemble them or use trigger locks.

"We're very pleased the case will go to the Supreme Court," said Alan Gura, an attorney for the residents. "We believe it will hear the case and will affirm that the Bill of Rights does protect the individual."

Singer said she will receive pro bono legal assistance from several high-profile constitutional law experts, including former acting solicitor general Walter E. Dellinger III. She called the city's handgun laws "reasonable" and said many handguns are used in illegal activities.

"This is not a law which takes away the rights to keep and bear arms," Dellinger said. "It regulates one kind of weapon: handguns."

Singer said she will ask for a 30-day extension to file the District's appeal with the Supreme Court, which would push the deadline to Sept. 5. The city's handgun laws will remain in effect throughout the appeal, Singer said.

"If the U.S. Supreme Court decides to hear this case, it could produce the most significant Second Amendment ruling in our history," Paul Helmke, president of the Brady Center to Prevent Gun Violence, said in a statement. "If the U.S. Supreme Court follows the words of the U.S. Constitution and the Court's own precedents, it should reverse the Appeals Court ruling and allow the District's law to stand."