A ten-year ban on some forms of semi-automatic firearms commonly referred to as assault weapons expires in the United States Tuesday. An effort to renew the ban stalled in Congress earlier this year. Debate on the efficacy and wisdom of the ban is far from decided.

In his 1994 State of the Union Address to Congress, then-President Bill Clinton made an impassioned plea for legislation to ban high-powered rapid-fire guns often used in violent crime.

"There is no sporting purpose on earth that should stop the U.S. Congress from banishing the assault weapons that out-gun police and cut down children!"

Months later, Congress acted and President Clinton signed the federal assault weapons ban that barred 19 types of semi-automatic firearms with features such as flash suppressers, bayonet attachments and high-capacity ammunition magazines.

But the legislation had a 10-year lifespan. Monday, as the law was to expire, gun control advocates held a news conference outside Washington. Maryland trauma surgeon Danny Westerban said he has witnessed the carnage that assault weapons can inflict.

"On far too many occasions I have been called in to try to save the lives of patients suffering from the devastating effects of these lethal weapons," he said. "As a trauma surgeon, I can tell you that when these weapons are used against a human being, they create injuries of such magnitude that they leave the victim with little chance of survival, even in our countries best trauma centers."

Maryland State Delegate Bill Bronrott said military-style weapons have but one purpose: to kill and maim humans. "These deadly military-style weapons have no place in a civil society. They are people-killers and cop-killers, not merely for hunting and sporting," he said.

Backers of the assault weapons ban are predicting a spike in deadly firearms sales in the United States, with increases in violent crime sure to follow.

John Lott of the Washington-based American Enterprise Institute disagrees. "I do not think there is going to be any change in crime. Not a big increase, I do not think you are even going to see a small increase," he said.

The Justice Department says violent crime is currently at a 30-year low in the United States, with incidents-per-1,000 citizens less than half the rate reported in 1993, the year before the assault weapon ban's enactment.

But John Lott, who has written several books on the relationship between gun control and criminal activity, says there were other actions taken in the 1990s that explain the drop in violent crime. Specifically, he points to tougher sentencing guidelines, reinstating the federal death penalty, putting more policemen on America's streets and requiring background checks of all gun purchasers.

"There are a lot of things that affect crime: arrest rates by police are the most important action for reducing crime, followed by conviction rates and longer prison sentences," he said.

Mr. Lott adds that the assault weapons ban had little practical effect, as gun manufacturers responded to the legislation by developing firearms that had none of the features banned by federal law, but that still retained the rapid-fire capability of semi-automatic weapons.

Even gun control advocates concede the assault weapons ban was flawed. But they contend it has been better than nothing. Jim Kessler of Americans for Gun Safety says the nation is less at risk from violent crime than it was 10 years ago, and that the ban on assault weapons should be preserved.

"The amount of progress that was made on the crime issue has been absolutely remarkable. I find it shocking that we would change even one iota, or take anything we did in 1993 and 1994 to solve this runaway national American problem," he said.

Mr. Kessler says more than 1,000 police chiefs across the United States have spoken out in favor of renewing the assault weapons ban.