City law enforcement officials foiled a plan to kill a police officer allegedly masterminded from inside the Rikers Island jail and two men are being charged in the plot, Commissioner Raymond Kelly said.

The police department and the Queens district attorney’s office received information from an informant inside the jail that inmate Andrew Spencer was allegedly devising a scheme to kill a police officer who was to testify against him on gun and assault charges, officials said.

An undercover police officer then went into Rikers Island jail and, posing as a hit man, secretly taped a series of conversations with Mr. Spencer, in which Mr. Spencer allegedly laid out his plans for the assassination, Mr. Kelly said.

On April 21, Mr. Spencer allegedly offered the undercover officer $1,000 and two automobiles — a Lexus and a Jeep — to murder the officer, the Queens District Attorney, Richard Brown, said. Mr. Spencer also allegedly told the undercover officer that an accomplice, Kiyee Kye, would supply weapons for the crime, the office said.

Police executed a search warrant at Mr. Kye’s home last week; a handgun and an assault rifle were discovered there, the office charged.

Messrs. Spencer and Kye are being charged with conspiracy to commit murder. If convicted, they face up to 25 years in prison.

The officer whom Mr. Spencer allegedly plotted to murder was not identified; Mr. Spencer was arrested in August 2006, when he was allegedly seen waving a loaded gun during a violent confrontation with another man, the office said. After obeying the officer’s demands to drop the weapon, Mr. Spencer allegedly attempted to bribe the officer with cash, the office added. Mr. Spencer was arraigned on gun and assault charges.