"Blood sport," federal prosecutors called it, and if they prevail in an indictment made public Thursday, the men who promoted it are in for a transformation - from prison officers to inmates.

After nearly 31/2 years of investigation, a federal grand jury charged the officers who worked at Corcoran State Prison in Kings County with setting up fights between gang rivals on the concrete yards of the institution's Security Housing Unit from January to June in 1994.On one occasion, officers shot and killed an inmate when the violence got out of control, the indictment said.

"The law gave these correctional officers the power to protect, but they used it instead to torment," U.S. Attorney Paul Seave said at a news conference Thursday in his Capitol Mall office. "These defendants used their authority to sponsor blood sport. In the process, they abused their power, and they abused the public trust."

The California Correctional Peace Officers Association and lawyers for two of the indicted officers who were contacted Thursday called the indictments politically motivated and said they would vigorously contest the charges if and when their clients are brought to trial.

"I am saddened and disheartened that the U.S. attorney is wasting the resources of their office and untold tax dollars on a frivolous and specious criminal prosecution," said San Francisco lawyer Michael Rains, who is representing Christopher Bethea, the officer who shot and killed inmate Preston Tate on April 2, 1994.

"There is absolutely no basis for it. These are all fine, veteran, dedicated officers," he said. "There was no conspiracy other than to do their job."

The indictment charges the officers with conspiring to violate the inmates' constitutional protections against cruel and unusual punishment. The officers are also accused of aiding and abetting each other in the alleged deprivations. One officer is accused of lying to the grand jury.

Officials said they could not recall any previous indictment against California prison employees similar in magnitude to Thursday's.

In a particularly stinging blast at the state Department of Corrections, the special agent in charge of the local FBI office, James Maddock, said his agency conducted the probe "despite intentional efforts by some correctional officers and other officials to stymie, delay and obstruct our inquiry." Maddock declined to elaborate.

Catherine Campbell, a Fresno attorney representing Preston Tate's family in a lawsuit, said she has been given 13,000 pages of documents from the prison system's own investigation into the prison. She said the documents indicated that of the "hundreds" of officers questioned by Corrections investigators, 46 percent "refused to talk."

According to the indictment, the officers unlocked inmates from rival prison gangs and released them onto the handball court-size exercise yards in the Corcoran SHU "when they knew of a substantial risk that those inmates would be physically assaulted."

The fights were set up "for the entertainment of correctional employees and for other reasons," the indictment said.