SACRAMENTO . (AP) — A federal judge on Wednesday struggled with how to gauge whether conditions for mentally ill inmates in California prisons have improved enough under federal oversight to return control of the facilities to the state, as Gov. Jerry Brown is seeking.

Lawyers for California argued in court that after 18 years of federal oversight and billions of dollars in state spending, the care now meets the requirements of the U.S. Constitution. Attorneys for inmates contend more improvement is needed.

U.S. District Judge Lawrence Karlton said he was torn by what standard to use in deciding when to end the federal court oversight, which he said has clearly forced California to improve what had been a substandard system.

"Clearly, the Constitution does not require perfection," Karlton said.

But if perfection is not the test, he said, "at what level can the court, must the court say, Oh, yes, it's not perfect ... but it's good enough for government work? It's good enough for the Constitution's definition of what the government must do."

California Deputy Attorney General Patrick McKinney said that's exactly the position the state is now in.

"The state has never argued that the system is perfect or that it needs to be," he told the judge. "Federal oversight should not continue unless there is a violation of federal law."

Inmates' attorney Michael Bien disagreed: "We have established that there are ongoing constitutional violations" he told the judge.

California has spent more than $1 billion to build mental health facilities and increase salaries to hire more qualified mental health workers. The state now has more than 1,700 psychiatrists, psychologists, therapists, social workers and nurses to treat more than 32,000 mentally ill inmates.

That amounts to about one specialist for every 19 patients.

Ending the lawsuit is key to the Democratic governor's attempt to lift a separate court order over prison crowding that otherwise will force the state to reduce its inmate population by nearly 10,000 by year's end.

The order, upheld by the U.S. Supreme Court in 2011, prompted the state to enact Brown's so-called realignment law, which requires lower-level offenders to serve their sentences in county jails. Since then, the population of the state's 33 adult prisons has dropped by nearly 25,000 inmates to about 119,000.

Karlton said Wednesday that the current prison system is "a substantial improvement over what the court found when it found deliberate indifference initially."

The question is whether the state can prove that the level of care now being provided complies with the Constitution, he said.

In a court filing, attorneys for the state said California has invested tremendous amounts of money, resources and effort to transform its prison mental health care system into one of the best in the country.

Lawyers for inmates say more mental health facilities must be built and staffed. They also say more must be done to reduce a suicide rate that exceeds the national average for state and federal prisons and worsened last year.

Karlton would have to rule on the request for renewed state control by early next month under a legal process Brown set in motion in January.

Court-appointed experts and overseers recently said California still provides substandard care to inmates with mental and physical illnesses, while federal judges have ruled against the state on virtually every motion it has filed.

The experts said they found 13 prisons they visited last year all provided acceptable mental health care.

Attorneys representing inmates complained that they were not notified of the visits and were not present when their mentally ill clients were interviewed, as required by ethical standards and a previous court order.

Karlton said the visits could constitute a "profound ethical violation" but indicated he may still allow the state reports because the case is so important.

The state said this week that a state expert had mentioned the interviews to one of the inmates' attorneys, and that the court-appointed special master was told that visits were planned.

McKinney repeated that assertion in court Wednesday, saying "we disagree that we violated the ethics."