Wanted: candidates for top jobs at Miami City Hall.

Just don’t expect to stay too long.

Since Mayor Tomás Regalado took office three years ago, turnover has become the norm. Miami has had four city managers, three police chiefs, and three budget directors. The capital improvements program has had four top bosses. Solid waste, human resources, risk assessment and general services have each had three directors.

The list goes on: Six out of 17 assistant city attorneys have left. The audit department turned over in 2011. Miami is currently seeking its third treasurer and its fourth finance director in three years.

Some recent high-level employees say they were pushed out after running afoul of the administration or city commission. Others left on their own volition, citing an uber-political work environment and less-than-professional management.

“People in the city don’t want to take leadership roles because they know they won’t last,” said David Mendez, who lost his job as assistant capital improvements director in 2010 after two decades in public service. “Every few years, the city has a bloodletting and directors are fired in an ignominious way. That affects morale.”

Beyond morale, the revolving door of directors has caused a dearth of institutional memory at the highest levels. And with consistency in short supply, departments have struggled to negotiate and close deals, like a $45 million bond issue needed to pay off a short-term bank loan. The city now finds itself under the gun, even though it has known for more than two years that the loan balance was due by January.

“You see it everywhere, from the city manager’s office to the finance department,” Commissioner Frank Carollo said. “There’s been a lot of turnover, and that’s caused some serious instability in the city.”

Many of those people are in positions for which the salary exceeds $100,000.

The latest departure: finance director Stephen Petty.

Petty, who drew an annual salary of $135,000, resigned last week, days after The Miami Herald reported that he lacked the qualifications for the job but had a connection to chief financial officer Janice Larned. Petty spent less than seven months on the payroll.

Petty wasn’t the only city hall staffer who was hired without meeting the minimum standards. At least 16 other employees, many in high-power posts, received qualification waivers in 2010 and 2011, city records show. City Manager Johnny Martinez has said that additional waivers may have been signed this year.

Supervisors in over their heads are unlikely to stick around, former Assistant City Manager Frank Rollason said.

“Those people get buffaloed,” Rollason said.

And people who do have the aptitude and the credentials, Rollason said, often want out.

Several former directors said they felt hamstrung by the mayor and manager, and feared being made a political scapegoat if they made a mistake. Some also said they were micromanaged by the commissioners, who are supposed to stay out of personnel decisions but can pressure the manager to fire someone.

“It’s very difficult for directors to function in an environment where the politics are so charged,” said former City Manager Tony Crapp Jr., who resigned in 2011 after six months in the job.

At least one termination became a political spectacle. Police Chief Miguel Exposito was fired in September 2011 after he defied city manager Martinez and demoted three high-ranking police officers.