Generous benefits, lax management and abuse of sick-leave policies have cost the Montgomery County government tens of millions of dollars in employee overtime pay, a study released Tuesday concludes.

The review, by the Montgomery County Council’s Office of Legislative Oversight, found that the county paid $63.3 million in overtime to 7,000 people from January 2011 through June 2012. That bill was driven up, researchers said, by vacation, sick and personal leave, and other time off provided under union contracts. Vacancies created by those absences are often filled at overtime rates.

Although there are wide variations among county agencies, employees are available for about 80 percent of the work year, or about 1,727 hours, researchers found. The average amount of some form of leave comes to 404 hours, or about 10 weeks.

About 70 percent of overtime costs were generated by fire and police agencies, which must provide staffing 24 hours a day. But the legislative oversight office found significant evidence that overtime and sick-leave policies are abused. More than 500 police and fire personnel were given overtime pay even though they had worked less than half the regular hours in a given pay period.

It suggests, researchers said, that personnel are calling in sick — receiving a paid sick day — and then filling at overtime rates for other officers or firefighters who are absent.

The report noted that unscheduled leave is a persistent problem across many departments and a major driver of overtime. “Staff report that it is not unusual for a person to be denied requested leave and then call in sick on the day leave was denied,” the report said. Another issue is repeated use of sick leave or vacation time before or after a holiday weekend.

Montgomery Fire Chief Richard Bowers pushed back at the findings Tuesday, saying the department was capable of controlling any abuse of sick leave. The problem, he said, is that there are not enough relief firefighters to fill vacancies at regular pay rates. The department must staff 35 fire and rescue stations.

“We wouldn’t need the overtime if we had proper staffing relief,” said Bowers, who will become Fairfax County’s fire chief next month.

The Department of Transportation, which operates the Ride On bus system, also suffers from high rates of unscheduled leave, the study said. There are many days when there are too few drivers to fill routes, forcing substitutes to be paid overtime.

Council members, who commissioned the report, expressed concern Tuesday and raised questions about the ability of County Executive Isiah Leggett (D) and his senior staff to control costs.

“It’s a wake-up call to management,” said council member George L. Leventhal (D-At Large). “Someone has to rein in these costs.”

Council member Phil Andrews (D-Gaithersburg-Rockville), who is running for county executive in 2014, said it was imperative to get a handle on overtime and leave policies, especially with new collective-bargaining agreements that will soon go before the council.

“The bottom line here is that for every five hours that county taxpayers pay for, employees are working about four of these, because leave is about 20 percent of total work hours,” Andrews said. “We need to understand these costs, because they are in the millions of dollars.”

Leggett, who has not announced whether he will seek a third term, acknowledged that curbing abuse of sick leave is something officials need to address. But he also said that cuts in the county workforce over the past few years have inevitably driven up overtime. “The problem is that in many cases, paying overtime is cheaper than hiring additional personnel,” he said.

He added that much of the leave time county employees have has been in collective-bargaining agreements since before he took office and that it would be “a real challenge” to extract.

The report, which will be the subject of a public hearing in a couple of weeks, was light on data comparing Montgomery’s overtime and leave policies with those of other counties in the region. It noted that the county generally offers more annual and personal leave in early years of service than do other jurisdictions. As years of service increase, the leave packages are more comparable to those of other counties.

But there are still differences that researchers said can add up to significant expenses. Montgomery firefighters, for example, receive 144 hours of annual sick leave, according to the study. Fairfax firefighters, who are not unionized, receive 104. Workers in Montgomery who do not hold public-safety jobs receive 120 hours of sick leave; in Fairfax, that amount is 104.