A group of Republican state lawmakers plan Thursday to appeal a federal court order that would force the state to reduce its prison population by 40,000 inmates, the legislators said at Capitol news conference.

Gov. Arnold Schwarzenegger, the main defendant in the two inmate lawsuits in which the order was issued, will also appeal the decision, his aides said. The appeals are separate.

The Republican lawmakers had previously joined the suit as interested parties. Assembly GOP leader Bruce Blakeslee of San Luis Obispo called the Aug. 4 order from the panel of three judges "an egregious overstep of federal power."

The judges said the state must come up with a plan by Sept. 18 to reduce the prison population because overcrowding has led to healthcare and mental health care that does not meet federal constitutional standards. One of the judges has said that in the past, inmates were dying preventable deaths at a rate of about once a week.

State Sen. George Runner (R-Lancaster) said the judges had ignored the state's recent "huge investment" in spending on inmate healthcare, as well as statistics showing that California spends more on healthcare per prisoner, and has a lower mortality rate among them, than many other states.

"We believe there is constitutional care today," he said. "We believe there always has been."