HARRISBURG — Smaller-than-expected payrolls for many school districts have left a surplus of state funds that could help ease Pennsylvania’s public pension woes and also undercut legislative support in the first test of Gov. Tom Corbett’s pension-reform agenda.

The state reimburses school districts for an average of 56 percent of their payrolls. If payrolls shrink, so do the payments.

In the year that ended June 30, $69 million of the state appropriation for school districts had not been spent. That money was earmarked for pension reimbursements, and the trend of shrinking payrolls appears to be continuing this year, according to the Public School Employees’ Retirement System, the statewide school employee pension fund.

So lawmakers could have an extra $140 million to spend as they scrutinize competing demands for scarce dollars in the state budget for the year that starts July 1, rough estimates by PSERS indicated. System officials cautioned Thursday that the amount of any surplus this year could vary according to payroll growth during the next three months.

Some legislators want to plow any such surplus back into the state’s share of pension costs instead of refinancing that obligation. Corbett has proposed refinancing to free up $175 million to help balance the 2013-14 budget and reduce the short-term cost to taxpayers. Many lawmakers are reluctant to revisit that strategy so soon after a similar refinancing in 2010.

Tapping the reimbursement surplus would provide the lion’s share of the savings from Corbett’s proposal with much less impact on other spending priorities or paying down debt, making it a politically attractive alternative to the only component of the governor’s plan that requires action this year.

“If that’s determined to be real money, I think you’ll see people coalesce around that,” said Steve Miskin, spokesman for the House GOP majority.

Drew Crompton, chief of staff to Senate President Pro Tempore Joe Scarnati, R-Jefferson, acknowledged that a sizable surplus of reimbursement money is “not a wild rumor,” but that he is still analyzing its political implications.

“It’s encouraging news and, if there were little reason for lawmakers to support Corbett’s pension plan before, there’s even less reason to do so now,” said Wythe Keever of the Pennsylvania State Education Association, the state’s largest teachers’ union.