A panel of federal judges today forcefully rejected a Schwarzenegger administration proposal to reduce prison overcrowding and threatened to impose its own plan for lowering the inmate population if the state does not submit an acceptable one within three weeks.

The judges said California officials had failed to comply with their order to produce a plan to pare the number of state prisoners by 40,000 within two years. The panel agreed to postpone a decision on a request by inmates' lawyers to hold Gov. Arnold Schwarzenegger in contempt of court for defying the earlier order, issued Aug. 4.

The state's plan, submitted last month, also failed to specify how much lower the number of inmates would be after six, 12, 18 and 24 months, as the judges had requested.

"We will view with the utmost seriousness any further failure to comply with our orders," said the seven-page decision by U.S. District Judges Thelton Henderson and Lawrence Karlton and 9th U.S. Circuit Court of Appeals Judge Stephen Reinhardt. That would leave the court "with no alternative but to develop a plan independently and order it implemented forthwith."

A Schwarzenegger spokeswoman, Rachel Arrezola, said the state would respond to the order by its Nov. 12 deadline. She said the administration is continuing to appeal to the U.S. Supreme Court the judges' "arbitrary" reduction order. That appeal was also filed last month.