For the second time in six years, the Mexican government has dismantled an elite federal anti-drug unit after discovering evidence that it had been corrupted by drug traffickers.

Closure of the Federal Special Prosecutor's Office for Drug Crimes followed simultaneous military raids last week on the agency's offices in 11 states. The raids began in Tijuana, where seven agents are accused of offering to return nearly five tons of seized marijuana, and two captured drug dealers, to drug lords in exchange for $2 million.

Attorney General Rafael Macedo de la Concha, whose office oversees the agency, said over the weekend that all 200 of the agency's employees are being questioned. He said the agency would be closed permanently and its functions transferred to an office charged with combating organized crime.

Macedo said the move was part of a restructuring to make the attorney general's office "a healthy institution." Since he took over in December 2000, more than 800 employees, many of them federal police officers, have been suspended, fired or charged with crimes. Another 1,300 are under investigation for corruption, he said.

The closed agency, roughly the equivalent of the U.S. Drug Enforcement Administration, was created in 1997. It replaced a similar agency that was dismantled after its director, Army Gen. Jesus Gutierrez Rebollo, was discovered to be on the payroll of Amado Carrillo Fuentes, one of Mexico's most notorious drug lords. He was convicted and is serving a 71-year prison sentence.

"We are not going to rest until these federal agencies have been totally cleaned up," said President Vicente Fox, who has promised a "war without mercy" on organized crime.

U.S. officials welcomed the agency's closure and said it was further evidence that Fox was serious about attacking Mexico's drug cartels. Fox has won high marks from many law enforcement officials for key blows against drug lords, including last year's arrest of Benjamin Arellano Felix, the reputed head of the ultra-violent Tijuana cartel bearing his family name.

"I like what I see," said Donald J. Thornhill Jr., a spokesman for the DEA in San Diego who has worked with Mexican officials for many years. "I think the Fox administration is sincere about addressing systemic corruption."

Despite praise for the swift dismantling of the agency, its demise was another sobering reminder that virtually no Mexican anti-drug agency has remained free of infiltration by powerful drug gangs.

The closure of the anti-drug agency is further evidence of the expanding role of the Mexican military in counter-drug efforts, which has provoked mixed reactions.

Macedo de la Concha is a former army general and has surrounded himself with key advisers from the military, to which he maintains close ties. Since he took over two years ago, the attorney general's office has coordinated activities closely with the military. Arellano Felix, for example, was arrested by elite military commandos, then turned over to Macedo's investigators for questioning.

While many praise the military's anti-drug efforts, others worry that too much responsibility is being given to an institution with scant public oversight. By tradition, the Mexican military operates largely autonomously. While Fox is commander in chief, many of the military's basic functions, including its budgets and military justice, remain beyond civilian or public scrutiny.

"Because it's such a hermetically sealed institution and seems to be unwilling to open up to public scrutiny, we think it's risky to give it more control and authority over the anti-drug efforts," said Eric Olson, a Mexico specialist at Amnesty International in Washington.

Olson noted that the military has had its share of drug-related corruption, including the arrest of Gutierrez Rebollo. Two other generals, Mario Arturo Acosta Chaparro and Francisco Quiroz Hermosillo, are currently imprisoned on drug charges.

Mexican President Vicente Fox has promised "war without mercy" on drug traffickers.