Fairfax County School Superintendent Karen Garza speaks during a news conference April 18, 2013. (Donnie Biggs/Fairfax County Public Schools)

A moment of truth will arrive for Fairfax County and its vaunted school system next week, when the county executive unveils a proposed budget that will attempt to cover projected shortfalls totaling $97.1 million over the next two years.

Facing higher pension costs and a drop in commercial tax revenue, the county board of supervisors is being pressured by the school system for an additional $97 million in funding in fiscal 2015 to help balance its own recently approved $2.5 billion budget.

The county, which directs about half of its budget toward the 184,000-student school system, has repeatedly said that it can’t increase school funding by more than about $34 million without cutting services for libraries and other programs.

Those tensions will be on display when school groups plan to rally outside the Fairfax County government center Tuesday before County Executive Edward Long delivers his advertised budget.

In a November preview for fiscal years 2015 and 2016, Long said that Fairfax has seen drops in revenue from sales taxes, hotel taxes and taxes on professional licenses — much of that stemming from federal sequestration cuts.

Fairfax has recently seen a rebound in its housing market, which may add extra property tax dollars through higher assessments, officials said.

But with lower-than-projected state education dollars expected from Richmond, that increase isn’t likely to be enough to provide more comfort for the schools.

“Fiscal Year 2015 is shaping up to be a challenging budget,” Sharon Bulova, chairman of the board of supervisors, said Friday in an e-mailed statement. “Managing expectations while also being sensitive to our taxpayers will not be easy.”