WASHINGTON - In an effort to stem the illicit flow of firearms into Mexico, the Justice Department announced Monday that all gun shops in the four Southwest border states will be required to alert the federal government to frequent buyers of high-powered rifles.

Deputy Attorney General James Cole said the new reporting measure will improve the ATF's ability to disrupt weapons-trafficking networks that funnel firearms to criminal organizations.

The new policy comes amid criticism of a flawed federal probe aimed at dismantling large-scale arms-trafficking networks along the Arizona border with Mexico.

In the probe, called Operation Fast and Furious, several agents with the Bureau of Alcohol, Tobacco, Firearms and Explosives say they were inexplicably ordered by superiors to stop tracking some small-time "straw" buyers who bought large numbers of firearms apparently destined for drug cartels.

Twenty low-level gun buyers have been charged in the operation. In December, two assault rifles turned up at the scene of a shootout that killed U.S. Border Patrol Agent Brian Terry. They were purchased by one of the now-indicted small-time buyers under scrutiny in Fast and Furious at a gun shop in Glendale.

In recent congressional testimony, ATF agent John Dodson estimated that 1,800 guns in Fast and Furious were unaccounted for and that about two-thirds are probably in Mexico.

Under the new policy, federal firearms licensees in Texas, California, Arizona and New Mexico must report purchases of two or more of some types of rifles by the same person in a five-day span. The requirement applies to purchases of semiautomatic rifles that have detachable magazines and a caliber greater than .22.

ATF estimates it will generate 18,000 reports a year.

Three gun-shop owners in Tucson said Monday that they doubt the new rule will create much of an additional burden.

"Not many people buy multiple rifles anyway," said Tom Rompel, owner of Black Weapons Armory, 5023 E. Fifth St.

But he and others viewed the new rule as unlikely to be effective, as well as discriminatory against firearms dealers in the Southwest.

"They're trying to deflect attention," Rompel said, referring to the controversy surrounding Operation Fast and Furious. "I think it's a cheap ploy on Obama's part."

Doug MacKinley, owner of Diamondback Police Supply, 170 S. Kolb Road, noted that licensed firearms dealers already have to report to ATF anyone who buys two handguns in a five-day period.

"Doing it on specific long guns isn't that big of a problem," he said. But he added, "I don't consider that it's going to be effective at all."

Josh Katz, owner of The Armory on Pima, 5118 E. Pima St., said he'll do whatever ATF requires.

"If the government says we need to follow a procedure, we'll be happy to do it," Katz said.

Rep. Elijah Cummings, the ranking Democrat on the House Oversight and Government Reform Committee, said the new policy "is exactly what ATF agents on the ground told Congress - that reporting multiple sales of military-grade assault firearms is a crucial tool to identify and disrupt Mexican drug cartels engaged in gun trafficking."

One of the critics of Operation Fast and Furious called the new policy "the height of hypocrisy." The Obama administration is restricting the gun rights of border state citizens, "when the administration knowingly and intentionally allowed guns to be trafficked into Mexico," said House Judiciary Committee Chairman Lamar Smith, R-Texas.

"Limiting the Second Amendment rights of law-abiding citizens is not going to solve the problem," Smith said.

Mexico's federal security spokesman, Alejandro Poire, praised Obama's action.

ATF estimates the requirement will cover nearly 8,500 gun store operators in the four states, though fewer than 30 percent of those operators are expected to have multiple sales to report.

ATF will retain the information, and if no investigative leads have been realized after two years, it will be purged.

Holders of federal firearms licenses already report multiple sales of handguns. The results go to the National Tracing Center, and ATF says it has led to successful prosecutions for firearms trafficking.

Star reporter Tim Steller contributed to this story.