By Tracy Weber and Charles Ornstein

Firms that supply temporary nurses to the nation's hospitals are taking perilous shortcuts in their screening and supervision, sometimes putting seriously ill patients in the hands of incompetent or impaired caregivers.

Emboldened by a chronic nursing shortage and scant regulation, the firms vie for their share of a free-wheeling, $4-billion industry. Some have become havens for nurses who hopscotch from place to place to avoid the consequences of their misconduct.

An investigation found dozens of instances in which staffing agencies skimped on background checks or ignored warnings from hospitals about sub-par nurses on their payrolls. Some hired nurses sight unseen, without even conducting an interview.

As a result, fill-in nurses with documented histories of poor care have fallen asleep on the job, failed to perform critical tests or stolen drugs intended to ease patients' pain or anxiety.

"A lot of them are really bad nurses," said Sandra Thompson, a nursing supervisor at Northridge Hospital Medical Center and Sherman Oaks Hospital, both in the San Fernando Valley. "Sometimes I see them here [at Northridge] and think, 'I wonder how long before I see them over' " at Sherman Oaks?

Some agencies are diligent about checking nurses' records, said Joey Ridenour, executive director of the Arizona State Board of Nursing.

Others are not. As a result, if wayward nurses want to work, "I think it's easier to hide in the registries," Ridenour said. "Some just sign them up."

Among reporters' findings, based on disciplinary records, personnel files, court documents and interviews:

* Firms hired nurses who had criminal records or left states where their licenses had been restricted or revoked. At least three firms employed a nurse in California whose license had been suspended in Minnesota for stealing drugs at a string of temp jobs. One used him after he'd been convicted of doing the same thing at a Santa Rosa nursing home.

* Temp agencies shuffled errant nurses from one hospital to another, even as complaints mounted. A Culver City agency continued sending one nurse to hospitals despite more than a dozen warnings that she was ignoring her patients and sleeping on the job. Before she was hired, the nurse had been convicted of 12 crimes, including prostitution, carrying a concealed weapon and possessing cocaine.

* Nurses who got in trouble at one agency had no problem landing a job at another. An Oklahoma nurse cycled through at least four Southern California agencies in a year, accused of pilfering drugs while at each. Before her final stop, she was arrested in her home state for calling in prescriptions while posing as a doctor's office employee.

Failings in the temp industry are magnified in states like California, where nurses are in particularly short supply. Almost every facility, from rural medical outposts to prestigious hospitals, must rely on temporary help.

Nearly 6% of registered nurses licensed in California -- or about 19,300 people -- are temps, based on a 2008 survey commissioned by the state. About half of these nurses live in other states.

Here, oversight of nurses in general has been weak. An investigation in July found years-long delays in disciplining nurses accused of serious misconduct. Regulators say they are working to fix the problems. Still, California's registered nursing board is among a minority that does not require hospitals, agencies or anyone else to report even serious lapses by nurses, including temps.

When staff nurses err, hospitals typically retrain or monitor them afterward. Temp nurses often are just exchanged for replacements, never receiving further guidance.

Industry executives and healthcare administrators say the firms are invaluable to hospitals and nursing homes, filling in for nurses who are sick or on strike and helping in swamped emergency rooms.

Nurses find the jobs attractive because they can see the country and control their schedules -- all while collecting premium wages, bonuses and sometimes travel and living expenses. Some work locally while others are employed by "travel" firms that send them all over the country. (They must have licenses in states where they work.)

"There are very good people who work registries who do not want to be tied to anything regular," said Katherine Eaves, chief nursing officer at Riverside County Regional Medical Center. "There's another group of people who are working registries because, guess what? They can't work anywhere else."

Many agencies leave it to applicants to reveal previous problems. Using multi-page checklists, they are asked to rate themselves on how well they manage critical care patients, use complex equipment and administer drugs.

Some nurses admit lying on applications or withholding information from their employers.