Prince William County supervisors approved an $890 million general fund budget Tuesday that raises taxes slightly but revives the road, park and library projects that were halted during the economic downturn.

The fiscal 2012 budget is based on a tax rate of $1.204 per $100 of assessed value, down slightly from what County Executive Melissa S. Peacor originally proposed. The average residential property tax bill will rise 2.5 percent, or $78. The fire and rescue levy was approved at 7.4 cents. Although residential bills will be higher than last year, they remain lower than they were in 2007, county officials said.

The adopted tax rate was not supported by Supervisors Michael C. May (R-Occoquan) and John T. Stirrup (R-Gainesville). The two voted for a lower rate that would not have funded additional police officers or park projects.

“I think we need to be more cautious in our approach,” May said. “I’m just not comfortable with the speed we are adding projects back into the budget.”

The budget supports the largest capital improvement program since at least 2007, county officials said. It will jump start all remaining road projects from the 2006 bond referendum and fund two new libraries in Gainesville and Montclair, the latter of which has been on the books for more than 20 years.

“Because of the spending reductions this board has made in the last four years, we can now start our capital improvement projects,” Prince William Board Chairman Corey A. Stewart (R- At Large) said, noting more than $200 million will go toward roads. “Time is money and people are stuck on the roads to this day. We have to continue to build roads because the state hasn’t.”

Under the adopted budget, Fuller Heights and Catharpin parks will get new soccer, football and baseball fields, Occoquan Park will be developed and more than $3 million in general and carryover funds will go to improve numerous trails in the county, including the Potomac Heritage National Scenic Trail.

The budget will boost the county police department, which will get 11 new officers plus be able to fill six vacant positions. The funding comes both from the county and the state.

Although the budget funds eight new positions for the county’s Department of Social Services, it is not as many positions as department officials had requested. Because of the downturn in the economy, department officials requested 13 positions, five of which would expire in 36 months, to support the increase in applications for assistance. The adopted budget has all eight positions expiring in three years.

Supervisor Frank J. Principi (D-Woodbridge) made a motion to add all 13 positions, but it failed. Social services officials said they won’t be able to meet state standards in terms of turnaround time for Medicaid applications and food assistance with the eight positions. But, they said, it is better than what they have now.

As part of the adoption, supervisors did approve a controversial change to the Virginia Retirement System. The 150 employees hired after July 1, 2010, will have to pay 5 percent of their salaries to the retirement system. The county funds the retirement system for all county employees, but a new policy adopted by the state allows the county to pass the cost on to new hires. Supervisors will discuss during the carryover process whether to give new employees a one-time 2.5 percent bonus to help offset their payment to the retirement system

The budget transfers $426 million to the schools, provides a 2 percent cost-of-living raise for employees, a 2 percent increase to county nonprofit organizations and an additional $30,000 for the free clinic — something requested by residents during the budget process.

The budget takes effect July 1.

“I think [this budget] is a good balance,” Stewart said. “This is a minor increase in the average residential tax bill and we are starting all these capital improvement projects.”