All 16 agreed to plead guilty to being part of a bribery and corruption conspiracy, said Noel Hillman, a Justice Department official.

Eleven defendants entered guilty pleas Thursday afternoon in U.S. District Court, acknowledging that they used their positions as uniformed public figures to assist in transporting cocaine for people they believed to be drug traffickers.

Two other defendants were scheduled to enter their pleas Friday with the remaining three on Monday, authorities said.

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Those who pleaded guilty were freed on their own recognizance. Justice Department prosecutor John W. Scott said all probably would start out facing sentences of 34 to 36 months for a single conspiracy count, but that the sentences could be less depending on the defendants' cooperation. He said he would ask for an indefinite delay in sentencing.

The defendants in the nearly 3 1/2-year-long sting were not arrested and agreed to cooperate with an investigation expected to bring more arrests and involve people from additional agencies, said Hillman and FBI Agent Jana D. Monroe, who is in charge of the bureau's operations in Arizona.

Hillman said the defendants drove cocaine shipments past checkpoints manned by the government while they wore official uniforms, carried identification and used official vehicles.

"Many individuals charged were sworn personnel having the task of protecting society and securing America's borders," Monroe said. "The importance of these tasks cannot be overstated and we cannot tolerate, nor can the American people afford, this type of corruption."

Hillman and Monroe said the FBI was tipped about an individual and set up the fake trafficking organization in December 2001. Military and police personnel then were lured with money to help distribute the cocaine or allow it to pass through checkpoints they were guarding, Hillman said.

Authorities engaged in an elaborate effort to determine that the defendants were predisposed to taking bribes, he said.

One defendant, John M. Castillo, 30, was on duty as an INS inspector at a border checkpoint in Nogales in April 2002 when he twice allowed a truck he believed was carrying at least 88 pounds of cocaine to enter the country without being inspected, Hillman said.

Castillo later sold INS documents to an undercover FBI agent that fraudulently provided for entry of undocumented immigrants into the United States, he said.

In another instance in 2002, several of those charged met an aircraft flown by undercover FBI agents that was carrying 132 pounds of cocaine at a remote desert airstrip, he added.

In full uniform, they supervised the loading of the cocaine into two military Humvees assigned to the National Guard and another government vehicle, then drove to a resort hotel in Phoenix - where another undercover agent posing as a trafficker paid them in cash, Hillman said.

The FBI used real cocaine seized in other operations, the officials said. The 16 suspects transported more than 1,230 pounds of cocaine, the officials said.

The cocaine, with a street value of nearly $18.5 million, never ultimately left FBI possession, officials said.

Also Thursday, a U.S. Border Patrol agent in Texas and his brother pleaded guilty to accepting about $1.5 million to allow drugs through a checkpoint.

Agent Juan Alvarez, 35, and his brother Jose Guadalupe Alvarez, 38, both of Laredo, pleaded guilty to conspiracy to bribe a public official and conspiracy to possess with intent to distribute marijuana and cocaine.

The brothers admitted they accepted money to allow drug dealers to move one or more loads of marijuana per month through the checkpoint between June 2003 and April 2005. Each load included 1 ton to 2 tons of marijuana. They also admitted to conspiring to move more than five kilograms of cocaine.

Conspiracy, the more serious count, carries a maximum sentence of 15 years in federal prison. The men also were jointly ordered to pay the government $1.5 million