W.House Curbing of Mexico Border Gun Rules Delayed

* Gun dealers in border states would report sales

* Delay comes amid gun lobby opposition

By Tim Gaynor

PHOENIX (Reuters) - A planned Obama administration clampdown on Mexico border gun dealers that would require them to report multiple assault rifle sales has been delayed by the White House amid stiff opposition from the powerful gun lobby.

The U.S. Bureau of Alcohol, Tobacco, Firearms and Explosives said last month it would tighten reporting requirements to help agents gather intelligence to target smugglers running high-powered rifles to Mexico, where 30,000 people have been killed in drug cartel violence since 2006.

The ATF measure would require around 8,500 gun dealers in Arizona, California, New Mexico and Texas to report sales of two or more semi-automatic rifles with detachable magazines to the same person within a five-day period.

The White House Office of Management and Budget was expected to approve the emergency rule change on Wednesday. But an official told Reuters that "ATF's information collection request is still under review," and declined further comment until the "deliberative phase is concluded."

The powerful National Rifle Association, which lobbies tirelessly for gun rights, has slammed the Obama administration for using Mexican cartel violence as a pretext to impose registration on gun sales.

"This is just a shallow excuse to engage in a sweeping firearms registration scheme," NRA executive vice president Wayne LaPierre said last month on the group's website.

"The NRA will do everything in its power to stop these 'emergency requirements' from taking effect," he added.

A BUREAUCRATIC DELAY?

Gun control activists said they hoped the delay was just procedural.

"We have been very disappointed with the Obama administration for most of its first two years in office with regard to the gun issue," said Paul Helmke, president of the Brady Campaign to Prevent Gun Violence.

"We're hopeful that this is just some standard bureaucratic delay. We haven't heard anything to the contrary," he added.

U.S. officials say an "iron river" of firearms flowing south to the drug cartels includes high-powered Kalashnikov and AR-15 rifles toted by cartel hitmen across Mexico, and decorative .38 caliber pistols popular with drug kingpins.

About 90 percent of the crime guns seized and traced in Mexico last year were initially sold in the United States, according to ATF. Investigators say around three-quarters of traces lead back to sales in the four border states.

Obama and the government of Mexican President Felipe Calderon have ramped up cooperation in recent months to curb drug smuggling heading north and to seize cash and guns flowing south to Mexico.

"Dealers are already required to report multiple sales of handguns and this is just implementing the same thing for long guns," Helmke told Reuters.

(Reporting by Tim Gaynor, editing by Greg McCune and Philip Barbara)