To save money in grim budgetary times, states nationwide have trimmed their prison populations by expanding parole programs and early releases. But the result — more convicted felons on the streets, not behind bars — has unleashed a backlash, and state officials now find themselves trying to maneuver between saving money and maintaining the public’s sense of safety.

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In February, lawmakers in Oregon temporarily suspended a program they had expanded last year to let prisoners, for good behavior, shorten their sentences (and to save $6 million) after an anticrime group aired radio advertisements portraying the outcomes in alarming tones. “A woman’s asleep in her own apartment,” a narrator said. “Suddenly, she’s attacked by a registered sex offender and convicted burglar.”

In Illinois, Gov. Patrick J. Quinn, a Democrat, described as “a big mistake” an early release program that sent some convicts who had committed violent crimes home from prison in a matter of weeks. Of more than 1,700 prisoners released over three months, more than 50 were soon accused of new violations.

An early release program in Colorado meant to save $19 million has scaled back its ambitions by $14 million after officials found far fewer prisoners than anticipated to be wise release risks. In more than five months, only 264 prisoners were released, though the program was designed to shrink the prison population by 2,600 over two years.

A victims’ rights group in California sued last month to block a state law that expands the credits prisoners can receive to shorten their sentences, and prosecutors in Michigan are challenging release decisions there.

“We’re not saying we shouldn’t reduce the prison population, but we’re saying you have to be very careful, and they’re making mistakes left, right and sideways,” said Jessica R. Cooper, the Oakland County prosecutor in Michigan, where the state prison population shrank by 3,200 inmates last year and where the parole rate is the highest in 16 years.

“You cannot measure those mistakes in terms of money,” Ms. Cooper said.

The changes in Michigan have been among the most pronounced, and they provide a glimpse into difficulties in about half the states, which have tinkered with parole, early release programs and sentencing laws or are considering doing so.

The authorities in some places say their changes are driven less by money than by the need to fix systems that are not working, and that such efforts were under way, in some cases, before the recession.

“We can live in fear and make bad policy based on fear,” said Patricia L. Caruso, director of the Michigan Department of Corrections, “or we can have some backbone and make policy based on what really helps our communities.”

Still, she said, the possibility that someone may reoffend always looms.

“I worry about it,” Ms. Caruso said. “I say a rosary every day.”

Gov. Jennifer M. Granholm of Michigan, a Democrat, has approved 133 commutations (more than some of her predecessors), expanded the state’s parole board to 15 members (allowing more cases to be considered), and recently proposed a budget that presumes 7,500 fewer prisoners next year for savings of more than $130 million.

But local prosecutors across the state are challenging at least 20 of the parole decisions, and Ms. Cooper has assigned two lawyers, full time, to review possible parolees from her county.

Among the 13,541 inmates released on parole in Michigan in 2009 was Scott W. Hankins, who had twice been convicted in sex cases and who had been accused by prosecutors of molesting other girls he had met at church, some of whom were developmentally disabled. The youngest girl, prosecutors say, was 7.

Mr. Hankins was most recently convicted in 2003 of first-degree criminal sexual conduct for touching a girl who, believing that his children would be present, had gone camping with him. He spent almost seven years behind bars until his release in November, meeting the minimum requirement of the range set by the sentencing judge. But the parole board’s decision to release him came well before the maximum of 30 years.

Psychologists who analyzed Mr. Hankins in 2009 said he met the criteria for pedophilia, court records say. He had a stellar attendance and homework record in prison treatment for sex offenders, but his responses, according to the psychologists’ report, indicated “that his insight into his actions is still in the development stage” and that he did not fully recognize how much he had hurt his victims.