SAN FRANCISCO, Sept 1 (Reuters) - California Gov. Arnold Schwarzenegger will appeal to the U.S. Supreme Court a federal court’s order that the state reduce its prison population by 40,000 inmates, a spokesman said on Tuesday.

The appeal will be a dramatic escalation in the long-running legal battle over the state of California’s overcrowded prisons and their often criticized medical care for inmates.

Schwarzenegger spokesman Aaron McLear said the appeal will be filed later this week, adding that cutting the state’s inmate population of about 170,000 must be done methodically and by state officials.

“We don’t believe it’s right,” McLear said, referring to the federal court order. “We need to reduce the prison population but we need to do so in a responsible way.”

Schwarzenegger is pressing for state legislation to cut the number of prisoners in order to bring down spending on prisons, one of the state’s top expenditures.

He backed a bill approved last month by the state Senate that would reduce the state’s prison population with a number of measures, including releasing elderly and ailing inmates. But the Assembly passed a rival and less ambitious bill on Monday, raising doubts the two bills can be reconciled.

A legislative battle over releasing prisoners may take shape amid public resistance to the idea after a sensational kidnapping case broke near San Francisco last week with the arrest of a paroled sex offender for abducting an 11-year-old girl, holding her for 18 years and having two children with her.