A man in jail on Rikers Island has been accused of trying to hire someone to behead Police Commissioner Raymond W. Kelly and to bomb Police Headquarters.

The police said the man, David Brown, 47, of Prospect Heights, Brooklyn, was charged yesterday with second-degree criminal solicitation in a plot that was discovered after the police received a tip on the department’s Crime Stoppers hot line on Feb. 13.

Not only did Mr. Brown offer to pay $15, 000 to have Mr. Kelly killed, the police said, but he also specified that he wanted him beheaded, the police said. He also offered to pay $50,000 to have the 14-story headquarters in Lower Manhattan bombed, though he was told that a job could cost upward of $150,000, the police said. It was unclear whether Mr. Brown had the resources to pay such fees, the police said. Mr. Brown is to be arraigned today in the Bronx.

In December, while he was in custody for violating an order of protection, Mr. Brown asked a fellow inmate to contact someone he could pay to kill Mr. Kelly, the police said. His request led an undercover officer posing as a contract killer to reach out to Mr. Brown, who has been convicted on a total of 30 charges, including 5 violent crimes, according to Paul J. Browne, the Police Department’s chief spokesman. In 2001, he was convicted of attempting to murder his wife, the police said.