The word “sustainable” is thrown around a lot these days in discussions of government spending, particularly by those who predict that a budget’s growth will outpace resources over time.

But can budget-cutting also be unsustainable? After three years without an increase, we think that Portland’s school budget is reaching that point. That’s why Portland voters should vote yes on the budget referendum on Tuesday.

The $94.2 million budget represents a 3.9 percent increase over the current year, and along with the city budget would result in a 2.9 percent increase in the tax rate, or an additional 54 cents per $1,000 of valuation. That would add $108 to the tax bill of the owner of a $200,000 home.

That kind of increase should not be made lightly, so it’s important to consider why the increase is necessary.

This is not the result of creeping program growth: The increase in local share results from the loss of temporary federal funds that were provided to schools during the financial crisis to prevent mass layoffs. Portland received $12 million over three years, and, as intended, the money allowed the school district to keep most of its employees working at a time when state revenues were in free-fall.

But that doesn’t mean that Portland did not make cuts. Portland schools shed 100 positions in order to keep budgets flat at a time when many costs were increasing.

The new spending is not being driven by increases in teacher pay, as has been suggested by members of the City Council and was reported in this newspaper.

The teachers are in the second year of a contract that contains no cost-of-living increase until 2014. Some teachers will receive raises for longevity or professional development, and those average out to a 1.9 percent raise overall. This coincides with the addition of five days to the school year with no extra pay.

It is the loss of temporary federal funds, not pay increases, that make this increase — the first in four years — necessary.

The question for voters, those with children in the schools and those without, is whether Portland can afford to keep cutting spending, or whether the austerity of the last few years is sustainable.

We think that it is not. This budget calls for strategic increases in areas that are important to the city as a whole. It expands preschool programs for 4-year-olds, making it more likely that they will enter school ready to learn. Research consistently shows that working with children before they start school heads off learning problems later.

That kind of investment in early childhood is tiny compared with the social costs that come due later when coping with adults whose educations went off track.

There is also an expansion of the adult education English learners program. Learning the language is a prerequisite to almost any job in Maine, and helping immigrants attain this basic skill is essential to their growth as productive members of the community.

As important as these programs are, it is vital that the school system maintains a rich and fertile learning environment for all the students in the elementary and secondary schools.

Families with children in school now can’t wait a few years for the economy to turn around. Their students need to learn now, and they need the teachers and tools to be able to do that.

Portland can’t afford to lag behind neighboring public schools, charter schools and private schools in the quality of its educational program if it is to maintain a diverse student body that includes families who have options to learn elsewhere.

If Portland becomes a school system only for those who have no other choice, the school system will fail, and with it, the city.

No homeowner likes a property tax hike, but a collapse of property values is just as bad, and that’s what happens to a community when its school system falls apart.

Out-of-control spending puts one kind of strain on a community. Failure to adequately fund schools is another. Neither is sustainable.

Portland voters should go to the polls Tuesday and support this school budget.No homeowner likes a property tax hike, but a collapse of property values is just as bad, and that’s what happens to a community when its school system falls apart.