More than 62,000 guns disappeared from U.S. firearm dealers' inventories in the past three years without any record that they were sold, according to a report by the Bureau of Alcohol, Tobacco, Firearms and Explosives.
The estimate means that dealers "lost" on average 56 firearms a day between 2008 and 2010.
In some cases, the weapons could have been stolen or sold under the table or on the black market, circumventing established registration procedures and background checks. They also could simply appear missing after legal sales because of a paperwork or administrative error.
"Missing firearms directly impact law enforcement officials' ability to reduce violent crime," said ATF assistant director for enforcement programs Arthur Herbert. "The inability to identify the retail purchaser of a gun used in violent crime removes the opportunity to secure a lead for where the gun has traveled."
Paul Helmke, president and CEO of the Brady Center to Prevent Gun Violence, which favors stricter gun control, said the findings reveal an alarming gap in oversight of gun dealers.
"It's obvious these folks aren't losing inventory," he said. "They're selling it under the table or out the back door, feeding the criminal market."
A spokesman for the ATF cautioned, however, that there is no evidence linking the missing firearms to illicit sales.
The Brady Center first publicized the numbers Wednesday after they appeared in a public ATF slideshow presentation at a Las Vegas trade show last week.
Both Helmke and a spokesman for the ATF said the total number of "missing" firearms likely understates the number of weapons without records of sale.
The agency, which has approximately 600 inspectors, performs compliance inspections at just 20 percent of the more than 60,000 U.S. retail gun dealers each year.
"The ATF doesn't have the staffing, the manpower, the money or the authority to do what it needs to do," Helmke said. "And they haven't had a full-time director since 2006."
In 2010, ATF reviewed 10,500 dealer inventories, resulting in the determination that 21,000 guns were unaccounted for.
Dealers who improperly complete licensing forms or fail to report multiple handgun sales, among other violations, could face fines or have their retail licenses revoked. Sixty-seven dealers were shut down last year, according to the data.
The agency also said investigators successfully accounted for more than 66,000 guns that had previously been listed as missing.
A spokesman for the NRA did not immediately respond to ABC News' request for comment Wednesday.
"This report illustrates just how severely government is failing Americans who expect to be safe from dangerous weapons in the wrong hands, and just how important it is that we face this problem comprehensively and openly as a nation," said New York Democratic Rep. Carolyn McCarthy, a vocal gun control advocate.
"It's not just high-profile incidents like Tucson, Virginia Tech and Columbine that we have to worry about -- the illegal trafficking of guns is a daily tragedy and daily security risk in America."
Federal law prohibits the ATF from requiring gun dealers to keep and report an annual inventory of their weapons. Audits by federal agents are allowed, but not more than once per year without a warrant.
McCarthy is one of several lawmakers, including some Republicans, who have proposed new legislation strengthening U.S. laws on the sale and tracking of guns in the wake of the Tucson shootings.
A number of recent national public opinion polls show Americans narrowly divided on greater federal regulation of guns.
In an October Gallup poll, 44 percent of Americans favored stricter gun laws, tying a record low, down from 78 percent from when the question was first posed in 1990.