A comprehensive study released yesterday by the National Academy of Sciences says a major national effort to improve knowledge about firearms is needed before anyone can judge the effectiveness of a variety of policies, from gun control to laws allowing people to carry concealed handguns.
The study, by the academy's National Research Council, found that accurate research on what works to reduce gun violence had been made impossible by a lack of information on gun ownership and by scholars' lack of access to information like the Bureau of Alcohol, Tobacco and Firearms' data on guns traced to crimes.
The National Rifle Association and its supporters in Congress have long opposed collecting information on gun ownership and sharing the bureau's gun-tracing data, describing such steps as an invasion of privacy.
Charles F. Wellford, chairman of the committee that wrote the report, said that among the major questions that need answers are whether gun violence could be better controlled if there were more restrictions on who can buy firearms, whether customers should be limited to buying one gun at a time and whether safety locks work.
''These and many related policy questions cannot be answered definitively because of large gaps in the existing science base,'' said Mr. Wellford, a professor of criminal justice at the University of Maryland. ''The available data are too weak to support strong conclusions.'' He spoke at a news conference in Washington, where the report was released.
The report was particularly skeptical of research claiming that homicide rates fall in states that pass laws permitting its citizens to carry concealed weapons. ''The committee found no credible evidence that the passage of right-to-carry laws decreases violent crime,'' it said.
Thirty-four states now have such laws, some of them based on research by John R. Lott Jr., a resident scholar at the American Enterprise Institute. Mr. Lott has written that allowing people to carry concealed weapons does reduce violent crime, but his findings have been disputed by many other researchers.
Andrew Arulanandam, a spokesman for the N.R.A., which supports the right to carry concealed weapons, said, ''I think these laws have been tremendously effective.''
Mr. Arulanandam said: ''This is not rocket science, but common sense. The whole purpose of these laws is to allow people to defend themselves when the need arises.''
The report also cast doubt on research about how often guns are used to deter crimes. Some research has found that guns are used 100,000 times a year to defend against a crime, but other research has put that figure as high as 2.5 million times a year, the report pointed out.
Such a wide variation calls the accuracy of the findings into doubt, leaving it unclear what is actually being measured, the study said.
But it also questioned some favorite findings by advocates of gun control. It said, for example, that there was not enough evidence to conclude, as gun control advocates say, that owning a gun increases the risk of a gun injury.
In addition, the report cast doubt on the effectiveness of some law enforcement programs to reduce gun violence that have been widely praised, like a Boston gun project in the 1990's that focused on juvenile gun possession, and Project Exile in Richmond, which gave stiffer federal sentences to criminals arrested in possession of a gun.
These programs seem to have reduced gun violence, but they were confined to a single city and there is not enough evidence that they could be replicated nationally, the report said.
''My sense is that people on both sides of the debate won't like the report,'' said Jens Ludwig, an associate professor of public policy at Georgetown University. ''The main thrust of it is, we don't know anything about anything, and more research is needed.''
The report was commissioned by the National Institute of Justice, a branch of the Justice Department; the federal Centers for Disease Control and Prevention; the Joyce Foundation; the Annie E. Casey Foundation; and the David and Lucile Packard Foundation.
ers a bunch of pansies.
