Carlos Canino, the Bureau of Alcohol, Tobacco, Firearms and Explosives acting attache to Mexico, greets Rep. Darrell Issa (R-Calif.) at a hearing on the controversial Fast and Furious operation. (KEVIN LAMARQUE/REUTERS)

A high-ranking official apologized Tuesday for mistakes made in a botched Arizona gun-trafficking operation during a congressional hearing in which lawmakers grilled federal agents about why they allowed more than 2,000 firearms to hit the streets in Mexico and the United States.

Deputy Assistant Director William McMahon, who oversees the western region of the Bureau of Alcohol, Tobacco, Firearms and Explosives, said the agency made mistakes in losing control of so many firearms during the controversial Operation Fast and Furious, which was intended to disrupt a Mexican drug cartel trafficking network.

“However good our intentions, regardless of our resource challenges, and notwithstanding the difficult legal hurdles we face in fighting firearms traffickers, we made mistakes,” McMahon told the House Committee on Oversight and Government Reform. “And for that I apologize.”

The packed hearing was the second held by Chairman Darrell Issa (R-Calif.), who, along with Sen. Charles E. Grassley (R-Iowa), is investigating allegations that ATF agents allowed 2,020 high-powered weapons, including AK-47s and .50-caliber sniper rifles, to “walk” to Mexico.

Fast and Furious, which began in Phoenix in November 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 individual illegal gun buyers, ATF officials testified Tuesday. The Justice Department’s inspector general had written a scathing report castigating ATF for not pursuing larger gun trafficking cases and spending too much time and resources on single “straw purchasers.”

Under the Phoenix plan, which was legally backed by Arizona U.S. Attorney Dennis Burke and funded by a Justice Department task force, agents followed, watched and documented straw purchasers who bought guns from Phoenix-area stores to see where the guns would eventually end up. One suspected trafficker illegally bought nearly 700 firearms during the operation. The agents also listened to a wiretap to try to gather intelligence about how the drug traffickers smuggled firearms into Mexico.

The most contentious questioning by lawmakers was of Bill Newell, a former ATF special agent in charge of the Phoenix field division who oversaw Fast and Furious. Newell insisted that he and his agents did not let guns “walk,” a street term for letting guns go rather than arresting the suspected traffickers. He defined gun walking as the agency actually putting a firearm into the hands of a criminal and letting it go.

Newell said the goal of the operation was to disrupt and dismantle an entire drug cartel. In hindsight, he said, he should have conducted more frequent “risk assessments” and regretted not pressing the Phoenix prosecutors to wrap up the case more quickly.

“It was not the purpose of the investigation to permit the transportation of firearms into Mexico,” Newell said.

An angry Issa snapped, “You’re entitled to your opinion, not to your facts.”

Some of the harshest criticism of Fast and Furious came from other ATF officials.

“The strategy . . . did not take into account the safety of the citizens of the United States and Mexico and blindly concentrated only on the goals of their investigation,” testified Lorren D. Leadmon, the leader of the AFT field intelligence support team for the Southwest border. “It is truly a sad time for each of us at ATF, and the impact of all this has been devastating.”

Darren Gil, a former ATF attache to Mexico, testified that he became concerned that large numbers of assault weapons traced back to Phoenix were showing up at Mexican crime scenes last year. Neither he nor any Mexican officials were told about the operation, he said.

Gil called his superiors in Washington and Phoenix and urged them to shut down any gun operation they might be running because of the mounting violence. When his frustration reached a boiling point, he got into a shouting match with his superior.

“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.”

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

“These guns went to ruthless criminals,” said Carlos Canino, the acting ATF attache to Mexico. “It infuriates me that people, including my law enforcement, diplomatic and military colleagues, may be killed or injured with these weapons.”