At the behest of President Clinton and gun control lobbyist Sarah Brady, the Senate recently voted to require that every firearm be sold with a lock. The next step is to require that all guns be locked up in the home - as is currently required in Washington, D.C., and in Canada, whose gun laws President Clinton has fulsomely praised. This next step will likely be taken when there is another horrible gun crime that (like the Littleton massacre) couldn't possibly have been prevented by a trigger lock. That crime will give the Republican congressional leadership another opportunity to make concessions that will immediately prompt the Democrats to escalate their demands for further concessions.

Are gun locks, as President Clinton says, a "no brainer"? Yes, indeed. The lock-up-the-guns proposal is great - as long as one doesn't think about it carefully.

Contrary to the impression created by sensationalist media, fatal firearms accidents involving children are far from common. In the United States, about half of all homes contain guns; the total gun supply is about 240 million, and there are tens of millions of children in the country. Yet according to the National Safety Council, in 1995 there were about 30 fatal gun deaths of kids aged 0 to 4 and fewer than 40 of kids aged 5 to 9. This shows that, even without legislation from Washington, the overwhelming majority of families with firearms already knows how to act responsibly.

Any parent knows that a single child's death is unspeakably tragic. Yet the number of toddlers who die from gun accidents is smaller than the number who die from drowning in buckets. And it's much lower than the 500 who die in swimming pools.

More generally, the total number of fatal accidents involving kids aged 0 to 14 in 1995 was 6,500, and fatal firearms accidents accounted for just three percent of the total. Yet the president is not scoring political points inveighing against bucket manufacturers, or demanding federal laws against unfenced pools on private property. Politics, not saving children's lives, is the foundation of the current anti-gun campaign.

But doesn't it make sense to require parents to keep guns locked if it will save even one child's life? Unfortunately, the analysis can't be that simple, because such a restriction will not only save lives; it would also cost lives.

President Clinton - and Liddy Dole at a recent speech at Yale, compare gun locks to "child-proof" safety caps on medicine bottles. It's a good comparison, because the safety caps increased accidental deaths, and gun locks would do the same.

According to research by Harvard's Kip Viscusi, the federal mandate about safety caps on medicine bottles made people more careless about storing medicine out of the reach of children. No cap can be really "child proof" (any bottle can be broken with a hammer), but careless parents left medicine bottles where children could get them, children defeated the "child-proof" caps and poisoning deaths increased.

Similarly, mandatory gun locks would encourage parents to stop being careful to keep loaded guns out of the reach of small children.

Even worse, many kinds of gun locks (such as locks that fit on the trigger), could cause accidents for both children and adults. A modern firearm won't discharge if it is dropped accidentally; but if the firearm has a trigger lock on it, the firearm often does discharge. That's why lock manufacturers warn consumers never to use the lock on a loaded gun. Mandatory use of locks could thus undo 50 years of improvements in firearms design that have helped reduce gun accidents by more than 75 percent.

In addition to increasing gun accidents, mandatory locks would likely increase deaths from crime. Guns are used quite commonly in self-defense; estimates of defensive gun uses per year range from 110,000 (National Crime Victimization Survey) to 1.5 million to 2.5 million or more (studies by criminologists Gary Kleck and Philip Cook). A very large majority of defensive uses simply involve display of the firearm (without a shot being fired), followed by the criminal's hasty retreat. Nobody knows what the exact count is or how many of those uses save the lives of kids or other innocents.

Nor does anyone know how many of those defensive uses would have been frustrated by potential crime victims having to fumble with trigger locks or safes - perhaps in the dark while an intruder advanced toward a child's room. But we do know what happens in countries like Canada where the laws require that firearms be locked up: the burglary rate is significantly higher than in the United States. U.S. burglars almost always avoid occupied homes, for fear of being shot. But Canadian burglars are three times more likely than American burglars to break into a home when people are there. From the Canadian burglar's viewpoint, a "hot burglary" (victims present) is often superior, since the alarm system will be turned off and there will be wallets and purses to grab.

Of course many burglaries of occupied homes turn into assaults or rapes perpetrated against the victim, and some turn into murders.

You might wonder how President Clinton and Mrs. Brady account for all this extra danger caused by gun lock laws. The answer is that they don't care, because they do not support defensive gun use (except by government employees, such as the president's bodyguards).

Although President Clinton claims that his gun control proposals won't cause too much trouble for hunters or target shooters (true), he does not claim that his laws won't substantially interfere with defensive gun use. Mrs. Brady told the Tampa Tribune in 1993, "To me, the only legitimate reason for guns in civilian hands is for sporting purposes." If a person morally opposes defensive force, then making it impossible for innocent people to defend themselves counts as progress.

If a family with small children lives in a safe neighborhood, then keeping the guns locked up may indeed be the safest choice. But if a family must live in a dangerous neighborhood, and if the parents have taught gun safety to responsible older children, then having the gun ready for immediate protection might be safer. Parents, not members of Congress, are best suited to make these kinds of decisions.

[*] Dave Kopel teaches law at New York University Law School, and Eugene Volokh teaches at UCLA Law School. Printed with permission from The Cato Institute.