By Pat Loeb and Diana Rocco

PHILADELPHIA (CBS) -- Mayor Nutter today praised the Philadelphia school district’s five-year plan (see related story) as “stark but realistic” and used the occasion to once more lobby for approval of a new property tax assessment system.

He concedes that some of the school cuts will be difficult but says the district’s future requires “shared sacrifice.”

Mayor Nutter says closing schools and controlling costs are essential, but more revenue is also needed –  revenue he says would come from the so-called “Actual Value Initiative,” a system that will tax real estate based on a new assessment — now under way — of its true market value (see related story).

“You cannot escape that,” he said today.  “You can’t kick that can down the road, and if we don’t take significant action the system will collapse.  Now, if you care about kids and if you care about education, if you care about the future of the city, that’s what we need to all grow up and deal with.”

The mayor expects tax collections will increase by $90 million, which he says reflects the increase in property values since the last assessment, in 2004.

Without it, he says, the school system could collapse.

“We need stable, secure, and appropriate funding for public education, for the children of our city and for our destiny — our common, shared future.”