When assault weapons from Phoenix showed up in large numbers at Mexican crime scenes last year, federal agents posted in Mexico City called their superiors in Washington and Phoenix and urged them to shut down any gun operation they might be running because of the mounting violence.

But their concerns were brushed aside, according to a new report that will be released Tuesday by Republican lawmakers. The report follows a congressional investigation of the controversial gunrunning sting, known as Operation Fast and Furious, that was overseen by the Phoenix office of the Bureau of Alcohol, Tobacco, Firearms and Explosives.

The frustration of Darren Gil, the former ATF attache to Mexico, reached such a boiling point that he got into a screaming match with his superior about the large volume of AK-47 variants and .50-caliber sniper rifles recovered at Mexican crime scenes and traced back to the same Phoenix gun stores.

“Hey, when are they going to shut this, to put it bluntly, damn investigation down,” Gil recalled in congressional testimony. “We’re getting hurt down here.”

Gil, along with Carlos Canino, the acting ATF attache to Mexico, are scheduled to testify at 10 a.m. before the House Committee on Oversight and Government Reform. It is the second hearing on Fast and Furious in an investigation started by committee chairman Darrell Issa (R-Calif.) and Sen. Charles E. Grassley (R-Iowa), ranking member of the Senate Judiciary Committee. Also scheduled to testify at the hearing are several top ATF officials, including Assistant Director William McMahon and Bill Newell, former special agent in charge of the Phoenix field division, which oversaw Fast and Furious.

Fast and Furious, a 15-month operation that began in fall 2009, was an effort by ATF officials to implement a Justice Department strategy that focused on identifying and investigating Mexican drug cartel networks, rather than just arresting gun buyers.

Under the Phoenix plan, which was backed by Arizona U.S. Attorney Dennis Burke and funded by a Justice Department task force, agents watched and documented “straw purchasers” who bought guns from Phoenix area stores, to see where the guns would eventually end up. They also listened to a wiretap to get intelligence about how the drug traffickers smuggled firearms into Mexico.

Some ATF officials praise the operation as one of the agency’s best because it gathered critical intelligence about drug cartels, especially the Sinaloa cartel, Mexico’s largest and most powerful drug trafficking organization.

But a mutiny by several agents on the case led to the congressional investigation by Grassley and Issa.

In the committees’ 60-page report released Tuesday, ATF officials in Mexico said neither ATF nor Justice, the parent agency of the firearms bureau, shared critical details about Fast and Furious with their own employees in Mexico or with Mexican officials.

“This is the perfect storm of idiocy,” Canino told investigators. “Never in my wildest dreams ever would I have thought that this was a technique. Never. Ever. It is inconceivable to me.”

Of the 2,020 firearms bought by straw purchasers during Fast and Furious, 227 have been recovered in Mexico, and 363 have been recovered in the United States. An additional 1,430 remain on the street.

The operation was halted after U.S. Border Patrol Agent Brian Terry was gunned down during a firefight in the Arizona desert on Dec. 14, 2010. Two AK-47 semi-automatic rifles recovered at the scene had been bought by one of the Fast and Furious suspects a year before.

“Unfortunately, there are hundreds of Brian Terrys probably in Mexico,” Canino said. “We ATF armed the [Sinaloa] cartel. It is disgusting.”