Attorney General Eduardo Medina said Ramirez accepted $450,000 from a member of the Pacific cartel, who offered to pay him monthly for alerting the drug gang to planned police operations. The cartel member, who was not identified, is cooperating with the investigation, Medina said.
Ramirez was named assistant attorney general for organized crime in 2006 when Calderon took office, and resigned in July at Medina's request.
Medina said the government is determined "to purge federal security and judicial institutions, identifying people who ... are involved in criminal activities and have abandoned the principles and values of public service."
"We will not betray the trust the President Felipe Calderon has given us," he added.
With this arrest, five top officials and two federal agents have been detained this year as part of "Operation Clean House," which targets officials who allegedly shared information with the Pacific cartel.
Ramirez was among those at the helm of Calderon's offensive to seize territory back from drug cartels, a two-year campaign that has deployed more than 25,000 army troops and federal police across the country.
Calderon has long acknowledged the probability of corruption among some officers involved in his offensive, which has led to the arrests of several kingpins but failed to contain surging violence that has grown ever more brutal, with drug gangs decapitating their rivals and staging daylight attacks on police and soldiers.
The government describes the Pacific cartel as an alliance headed by the Sinaloa drug gang.
Medina said the seven detained officers passed information to two cartel factions - those led by the Beltran Leyva brothers and by the Zambada brothers.
Medina offered no details on what information was leaked, or which operations may have been compromised. One of the Beltran Leyva brothers was arrested earlier this year despite the corruption, and last month, police arrested Jesus "The King" Zambada and 15 other alleged members of the Sinaloa cartel.
Ramirez was arrested Thursday after voluntarily speaking to investigators, and jailed pending an investigation on possible charges of involvement with organized crime.
Medina said Ramirez met twice with his Pacific cartel contact in Mexico City. At the second meeting, Ramirez was allegedly accompanied by two other directors of his agency's organized crime division. The two others, Miguel Angel Colorado and Fernando Rivera, also were arrested.
