U.S. authorities in Mexico charged with stemming the flow of U.S. weapons to drug cartels have been hampered by shortfalls in staffing, agents with limited Spanish skills and the difficulty of recruiting new agents to the dangerous posting because they may not officially carry weapons, current and former staff members say.

Facing new accusations that investigators with the federal Bureau of Alcohol, Tobacco, Firearms and Explosives allowed buyers to funnel high-powered assault weapons into Mexico, a senior agent posted to Mexico before 2010 said the agency has not fielded the resources necessary to block mass movements of weapons across the Southwest border.

These movements have come under scrutiny amid revelations that ATF investigators delayed for months the arrests of possible cartel gun buyers, allowing the flow of hundreds of weapons to Mexico in the hope of catching bigger buyers. The policy has outraged many agents and prompted a U.S. Senate investigation.

On Monday, most of the architects of the Phoenix-based operation, known as Fast and Furious, were called to Washington, D.C., to discuss the operation.

Acting ATF Director Kenneth E. Melson announced he will ask a panel of police professionals to review the bureau's firearms-trafficking strategies.

Rene Jaquez, a former ATF attache in Mexico City and deputy attache in Ciudad Juarez, said Monday that agents in Mexico do not have the resources to effectively run down gun smugglers.

"I can tell you from my perspective as the former country attache in Mexico . . . that ATF has not taken seriously its role in the international affairs program as far as Mexico is concerned," Jaquez said in an interview.

Jaquez said ATF field offices in Mexico are so short-staffed that agents are either forced to spend most of their time on paperwork or don't have necessary backup to safely do street work.

"It was one meeting after another. At the end of the week, you ask, 'What did I do?' And ultimately the question has to be asked, 'OK, ATF has put all this money into Mexico, what have we done? How many guns have we stopped from coming into the country?' Well, this whole scandal shows we've probably allowed more guns into the country than guns we've stopped," Jaquez said.

"The next question is, how many people have gone to jail compared to three years ago, when we had only three people there? The answer is, none. There is no difference," he said. "We have no prosecutions that have resulted from us being in Mexico City."

Other agents said there have been some prosecutions, but they are few because the agency has not deployed enough personnel to make a real dent in firearms trafficking.

Jaquez said that the agency was able recently to expand from its presence in Mexico City and Monterrey, opening satellite offices and electronic gun-tracing operations in eight other Mexican cities.

But Jaquez said he complained to ATF management that the new offices would be largely ineffective for mounting firearms investigations if they did not each include at least four agents and a supervisor. Some offices, he said, had only a single agent - sometimes one who didn't speak good Spanish.

"At (two of our offices) we have a non-Spanish speaker, and an iffy Spanish speaker," Jaquez said. "So how do you go out there and do anything, when ATF hasn't taken it seriously enough to even send Spanish speakers down to Mexico?"