DENVER (AP) _ A prosecutor asked a federal appeals court to reconsider a ruling that declared plea-bargained testimony illegal, saying the decision would paralyze the nation's criminal justice system.

During a 50-minute session Tuesday before all 12 judges of the 10th U.S. Circuit Court of Appeals, Michael Dreeben, a deputy solicitor general, cited sentencing guidelines and the witness protection program as evidence that witness agreements are legal.

The court is reconsidering a July ruling by three of its members that concluded federal law bans prosecutors from offering anything of value _ a reduction in charges, immunity or other incentives _ in exchange for testimony. A decision is not expected for several months.

If the ruling is upheld, it could affect criminal cases in Kansas, Colorado, Oklahoma, Utah, New Mexico and Wyoming. Judges in other circuits could adopt the decision, so the outcome is being watched closely nationwide.

``This decision, if it stood, would create enormous changes,'' said legal analyst Andrew Cohen, who observed the arguments.

Prosecutors believe deals offering leniency to witnesses who testify in criminal cases are the foundation of complicated cases that bring down organized crime leaders, drug lords and other high-profile criminals.

Defense attorneys contend the agreements are tantamount to buying testimony and argue that there are other ways witnesses can help prosecutors.

John Wachtel, a defense attorney whose appeal in a Kansas drug case led to the ruling, said defense attorneys lack the authority to give witnesses benefits in exchange for testimony, so a ban on such agreements ``levels the playing field.''

The ruling came in a Wichita case in which Sonya Singleton was convicted in 1997 of cocaine trafficking and money laundering after co-defendant Napoleon Douglas testified against her. She was sentenced to 46 months in prison.

In exchange, prosecutors promised they would not prosecute Douglas for other offenses and would tell the parole board and sentencing judge about his cooperation.

Ms. Singleton argued in her appeal that the district court erred by refusing to throw out Douglas' testimony. The panel agreed and granted her a new trial, but that decision was vacated a week later, pending the outcome of Tuesday's hearing.