Kilder Alvim's family has been selling guns, rifles and ammunition for 45 years in a small shopping plaza here in the world's 14th-largest city, where tropical beauty and molten violence exist side by side. He even has a picture on the wall of his 6-month-old daughter on a bed with a .45-caliber gun. It hangs next to an antique Smith & Wesson sign.

But the only sign that matters to him now is the one on his storefront that reads "Closed Because of the New Law." It is there because the government of Rio de Janeiro state has passed a revolutionary piece of legislation: One of the world's toughest weapons laws, it forbids gun vendors from selling firearms and related products to anyone but police, the military and private security forces.

The law, which went into effect last week, makes no exceptions for sportsmen or collectors. Alvim cannot even sell plastic ammunition boxes or gun cases. An amendment to the law currently being debated would go a step further and require all civilians who own guns legally to turn them in within a year -- possibly in exchange for compensation of about $90.

The action by the state's new, liberal government comes as the national legislature in Brasilia debates a similar law that would apply to all of Brazil -- a country where a higher percentage of people are killed by firearms than any place at peace except South Africa, according to a recent U.N. report. In Brazil, people are killed by guns at the rate of 25.78 per 100,000 deaths, compared with a rate of 6.24 per 100,000 deaths in the United States.

Though Alvim is opposed to the law, recent polls in Rio show more than 70 percent of respondents favor it. If a national disarmament law is approved -- which, many analysts say, is likely by year's end despite a late mobilization by a relatively weak gun lobby -- it would put Brazil, one of the hemisphere's most violent nations, alongside such countries as Britain and Australia as one of the world's leading practitioners of gun control.

"I believe we are all facing a decision at the turn of the century whether to continue down the path of barbarism or to move toward civilization," said Luiz Eduardo Soares, Rio de Janeiro state's undersecretary of security and architect of the new law. "By getting rid of guns, we in Rio are choosing civilization."

The new law, politicians in Rio say, reflects an evolution in efforts to combat crime in Brazil's most violent state. In the mid-1990s, then-Gov. Marcello Alencar adopted what some dubbed a "below zero tolerance" of crime. He initiated such policies as police pay raises for "acts of bravery" -- which, in practice, were killings of suspected criminals. This fueled more distrust of a police force renowned for corruption and violence. Human rights experts say the policy's main effect was an increase in violence.

Now, the liberal politicians voted into office last year are taking a different approach, deciding that the solution is to disarm Rio. And, standing in front of his locked counter of rifles and pistols, Alvim cannot believe it.

The gun lobby in Brazil "wasn't prepared or organized enough. This would never happen in the United States, because it would never be allowed by the good people of that country. Now we're going to be lambs for the slaughter. Do you think criminals get their guns legally? No way, man! They're going to have the guns and we won't."

Indeed, critics say that in a state where only 40 percent of the estimated 2 million guns were obtained legally, the law will do little to reduce violence and only make things worse.

Under the new law, buying a gun legally is subject to stringent regulations -- someone with even a traffic violation is forbidden from doing so -- and the guns permitted for sale are not as powerful or deadly as those popular among criminals.

The law requires those allowed to buy guns to wait two months or longer for background checks -- ensuring that a black market for guns will flourish, the law's opponents say.

Also, opponents say loopholes, such as the ability of Rio residents to obtain guns out of state, mean that the law will have little effect if someone is determined to buy a gun.

"We already have Draconian laws that force us to get everything short of the president's signature to buy a weapon," said Marcello G. Torres, director of international relations for the National Association of Firearm Owners and Merchants.

But supporters counter that the law is part of a wider plan to enforce peace. A position for an ombudsman has been created to oversee complaints about police brutality. A parallel campaign is being launched by a new gun-control department of the Rio police to "blitz" houses of suspected illegal weapons dealers and to cut down on illicit firearms.

Authorities are trying to close legal loopholes, partially by passing amendments to the law but also by supporting passage of a national law.

"This is also about trying to create a taboo, to stop the creation of a gun culture as it exists in the United States," said Ignacio Cano, an Institute for Religious Studies sociologist in Rio who analyzes violence. "By making gun purchasing illegal, we want to make it so parents will be embarrassed to tell their children they have guns. Because it will be admitting that they have done something against the law."