Six members of the Mexican government's top organized-crime unit have been arrested on suspicion of leaking information to drug traffickers, officials said Wednesday.

An official in the Mexican attorney general's office said a supervisor and five agents are thought to have passed tips to smugglers in the west-central state of Sinaloa for about three months.

The official, briefing reporters on condition of anonymity, said the men disclosed details about evidence that had been seized during government raids and information about arrestees. He said authorities were looking into possible involvement by other employees of the agency, known as SIEDO, its initials in Spanish.

SIEDO, which investigates drug and arms smuggling as well as kidnapping and terrorism cases, is well known and generally trusted by American law enforcement agencies.

Its agents have helped U.S. authorities build cases against Mexican drug suspects, such as members of the Tijuana-based Arellano Felix gang, by sharing intelligence and granting access to Mexican witnesses and their statements.

Confirmation that SIEDO was infiltrated by drug traffickers would be a black eye for the 400-member agency and for President Felipe Calderon's 20-month-old offensive against organized crime.

Mexico is awaiting $400 million in U.S. crime-fighting aid as the first installment in what the two nations describe as a stepped-up joint push to combat the flow of illegal drugs into the United States.

Deputy Atty. Gen. Noe Ramirez Mandujano resigned as SIEDO's chief two weeks ago as part of a shake-up that appeared tied to public anger over a persistent wave of kidnappings. The attorney general's office said the resignation was not tied to the current investigation. Previous efforts by Mexico to battle crime through highly touted specialized police units have fallen victim to suspected corruption. SIEDO's predecessor within the attorney general's office, an anti-drug agency known as FEADS, was shut down in 2003 after half a dozen of its agents were arrested on suspicion they were helping drug traffickers.

In the latest episode, authorities said they arrested SIEDO's technical coordinator, Miguel Angel Colorado Gonzalez, and five agents assigned to the agency by Mexico's equivalent of the FBI.

The men, though not privy to the most sensitive investigative details, had access to information about arrest orders and the timing of searches, and about the agency's security arrangements.

The attorney general's office said the six were arrested last week after an investigation that began months ago into possible leaks to the news media. A judge ordered the suspects detained for 40 days as the investigation advances.

The men allegedly provided tips to a Sinaloa trafficking gang led by the Beltran Leyva brothers.

The gang, once part of a loose alliance of Sinaloa smugglers known as the Federation, has been involved in a bloody fight with another leading Sinaloa trafficker, Joaquin "Shorty" Guzman, one of Mexico's most wanted fugitives. That feud has sparked months of slayings that have left more than 400 people dead in Sinaloa so far this year, according to government figures.

The Beltran Leyva faction is suspected by authorities of carrying out the assassination in May of the acting federal police chief, Edgar Millan Gomez, at his home in Mexico City.

ken.ellingwood@latimes.com