* Rule tells retailers to report multiple rifle sales
* Court doubts their claim that measure is burdensome
By David Ingram
WASHINGTON, Jan 9 (Reuters) - A federal appeals court signaled on Wednesday it was prepared to uphold a regulation designed to detect the sale of semi-automatic rifles to Mexican drug cartels, one of the few gun control measures put forward so far by the Obama administration.
Gun retailers and manufacturers, including a trade group based in Newtown, Connecticut, scene of the Dec. 14 school massacre, say the rule is burdensome and violates federal law.
It requires stores in the four U.S. states bordering Mexico to send a notice to federal law enforcement whenever someone buys two or more of rifles during any five-day period.
The measure applies only to high-caliber, semi-automatic rifles that can use a detachable magazine.
The U.S. Bureau of Alcohol, Tobacco, Firearms and Explosives (ATF), which regulates gun sales, adopted the rule in 2011 amid rising cartel violence and at the urging of gun control groups for President Barack Obama to act.
Thousands of firearms are thought to cross the border illegally into Mexico each year, and semi-automatic rifles with detachable magazines are a favorite of drug traffickers, the ATF said in a report last year.
Mexican authorities recovered more than 68,000 U.S.-sourced guns from 2007 to 2011, the ATF said.
The rule applies to retailers in Arizona, California, New Mexico and Texas who, perhaps without realizing it, could be sources for those firearms.
Gun stores "have to create a new system to keep track of that," Richard Gardiner, a lawyer for retailers Foothills Firearms LLC and J&G Sales Ltd, told the U.S. Court of Appeals for the District of Columbia Circuit.
Federal law does not allow law enforcement to require that system, he said, calling it burdensome because store workers do not always know which of the guns they sell are covered.
The court's three judges, though, repeatedly doubted whether the rule creates much additional work.
"I don't remember the record containing any evidence of confusion," said Judge Harry Edwards.
ATF has a special phone number for retailers to call if they have questions, such as whether the rule covers a particular rifle, but few people have called, government lawyer Michael Raab told the court.
"Any dealer worth his salt" should know whether most guns he sells fit the criteria, Raab said, echoing the wording of a lower court judge.
Gardiner responded that evidence of the rule's burden is unnecessary because it is a government overreach.
The court is expected to decide within the next few months.
Gun rights advocates have also argued that the ATF measure could lead to a federal database of guns, which they fear would infringe on their rights. Republicans in the U.S. House of Representatives have tried to cut off money to enforce the regulation.
The National Shooting Sports Foundation, a trade group for gunmakers and a plaintiff in the lawsuit, is based in Newtown, where gunman Adam Lanza killed his mother, 20 children and six school employees before shooting himself in one of the worst U.S. school shootings.
Lower court judges in Texas and Washington have upheld the ATF rule, which is an example of steps Obama can take outside the proposed gun control laws he is expected to send to Congress this month.
The case is National Shooting Sports Foundation Inc, et al, v. B. Todd Jones, U.S. Court of Appeals for the D.C. Circuit, No. 12-5009.