HARRISBURG — Pennsylvania’s poorest school districts, which usually get the most help from the state, will suffer the most pain if Gov. Tom Corbett’s budget is approved, according to advocates who say the plan will deliver a huge setback to efforts to erase educational disparities.

The difference in potential losses is eye-popping: a high of $885 per student in the tiny Union School District in Rimersburg and a low of $32 per student in York Suburban School District in south-central Pennsylvania, according to an analysis by the Philadelphia-based nonprofit Education Law Center of Pennsylvania, which advocates for poor and disadvantaged students.

If Corbett’s budget is enacted, it would take a decade to undo the damage that one such year of cuts would do to recent gains toward closing the education gap between wealthy and poor children, the law center’s Baruch Kintisch said.

“The cuts need to be distributed in a way that doesn’t slaughter the poor students in the state,” Kintisch said.

Corbett’s Department of Education did not respond to requests for comment.

Kintisch and others say the administration apparently flicked the reverse switch on a formula in state law that favors poorer districts in allocating billions of dollars annually to the state’s 500 school districts.

“The people who made the most tend to lose the most, that’s the unfortunate way of looking at it,” said Senate Appropriations Committee Chairman Jake Corman, R-Centre.

For now, lawmakers are just beginning to see how their school districts would be affected by Corbett’s two-week-old spending plan.

Whether lawmakers look to wipe out some of the cuts, or whether they choose to alter the way the cuts are distributed, remains to be seen.

Corman said discussions haven’t developed yet on the subject of whether the cuts should be distributed differently — for instance, on an across-the-board average reduction of $313 per student across the state, as Kintisch suggested.

“I don’t know how that would work through the formula, but everything is on the table for discussion at this point,” Corman said.

There is a long history of political tinkering with a state school funding formula that otherwise delivers proportionally more money to school districts with bigger hardships, such as more poverty and more children with special needs.

Last year, the Legislature produced a compromise that allowed each school district to get a minimum 2 percent increase — benefiting even wealthy and shrinking districts that might not otherwise have received any extra money. Such political deals have diverted hundreds of millions of dollars away from districts deemed by the funding formula to be more deserving, Kintisch said.

“In good years when there have been increases, the poor districts know that they’re still not getting their fair share, but nobody complains because everybody’s winning,” he said.

In keeping with his pledge to balance Pennsylvania’s budget without raising taxes or fees, Corbett made the cutbacks as part of his strategy to close Pennsylvania’s projected multibillion-dollar deficit for the 2011-12 fiscal year beginning July 1.

He would slash about $550 million, or about 10 percent, from the state’s primary subsidy for public school operations and instruction, and a total of more than $1 billion when counting his move to eliminate special grants that subsidized programs such as all-day kindergarten and reimbursements to school districts for services to charter school students.

Under Corbett’s plan, 73 districts would lose more than $600 per student in primary subsidies, while 49 districts would lose less than $100 per student, according to the law center’s analysis. The 73 districts that lose the most have an average poverty rate almost four times that of the 49 districts that lose the least, based on the group’s analysis.

The Fox Chapel School District in suburban Pittsburgh would lose $57 per student. Its neighbor, Pittsburgh, would lose 10 times that, or $581 per student. Pittsburgh’s student poverty rate is more than four times that of Fox Chapel’s.

The Derry Township School District in suburban Harrisburg would lose $45 per student. Not far away, the Steelton-Highspire School District would lose 14 times as much, or $631 per student. Steelton-Highspire’s student poverty rate is more than five times as high as Derry Township’s.