Gun-control advocates across the country reacted with shock and outrage at the Supreme Court’s decision to strike down the District of Columbia’s ban on handguns today, saying the ruling would threaten gun-control measures in other states.

If there was any doubt that other bans would be in peril, the National Rifle Association quickly put those questions to rest when it announced shortly after the ruling that it would file a flurry of lawsuits challenging restrictions in San Francisco, Chicago and several Chicago suburbs. The law in Washington, which spelled out rules for the storage of weapons and made it extremely difficult for most people in the district to legally possess a handgun, was among the strictest in the nation.

“I consider this the opening salvo in a step-by-step process of providing relief for law-abiding Americans everywhere that have been deprived of freedom,” Wayne LaPierre, the executive vice president of the N.R.A., said in a statement.

In its 5-to-4 decision, the court ruled that the Constitution protects an individual’s right to own guns, not just the right of the states to maintain regulated militias. It also said that the District of Columbia’s requirement that lawful weapons be disassembled or limited by trigger locks was unconstitutional because it made them virtually useless.