HARRISBURG - The Corbett administration and legislative leaders have struck a tentative deal on a $27.15 billion budget that restores some of the state's dwindling aid to public schools and state-related universities.

"We have, certainly, an agreement in principle," Senate Majority Leader Dominic Pileggi (R., Delaware) said late Thursday afternoon.

Pileggi said there were still unresolved issues, but he declined to elaborate. "We are working through them," he said.

Details - the kind many school districts, universities, hospitals and other agencies want to see - were scant Thursday.

It appeared that the sides agreed on a spending plan that does not raise or impose new taxes. It will not, for instance, include a levy on the extraction of natural gas from the Marcellus Shale, which had been pushed by a number of lawmakers as a way to add much-needed dollars to the state's coffers. This year, Pennsylvania is facing a projected $4 billion deficit.

That, in turn, could allow Corbett to say he kept his campaign pledge not to raise a single tax - although an influential, Washington-based antitax group is poised to challenge that assessment should the final budget include a provision to increase a fee paid by hospitals related to Medicaid subsidies.

The budget deal calls for using about half of the $550 million in higher-than-anticipated revenues the state gathered in April and May. Democrats had pushed for using all of it to offset steep cuts to public schools and higher education that Corbett had proposed in his budget blueprint this year.

Corbett had advocated squirreling it away or using it to pay down the state's debt.

In an interview late Thursday, Pileggi said some additional state funding would be steered to public schools, but not as much as he had hoped.

In his proposed budget, Corbett planned to wipe out more than $1 billion in basic education funding. That included zeroing out grants to districts for prekindergarten, full-day kindergarten, and class-size reduction in kindergarten through third grade.

The House GOP, in a budget counterproposal last month, had tried to restore some of that funding. The Republicans' plan would have increased by about $210 million state funding for kindergarten-through-12th-grade education.

The tentative deal struck Thursday pads that $210 million with additional dollars, Pileggi said, "but not as much as what I would have liked to see." He would not give details.

The budget deal also would increase funding for higher education, which Corbett would have dramatically cut.

The governor had proposed eliminating $625 million, or 52 percent, of state aid for the 18 state-supported colleges. In the budget compromise, those schools would end up taking about a 19 percent cut, legislative officials said.

The budget deal, as expected, cuts some funds to the Department of Public Welfare, but not as much as some legislators had wanted.

Still, an unexpected wrinkle Thursday came in the form of a letter from Grover Norquist, who heads the Washington-based group Americans for Tax Reform. Corbett signed the group's antitax pledge while running for governor. All together, 13 governors and 1,252 legislators across the country have signed the pledge, according to the group.

In the letter, Norquist writes that raising the hospital fee amounts to a new tax on medical care in Pennsylvania.

Hospitals began paying the assessment last year to help the state access additional federal funds - funds that, in turn, are used to boost hospitals' public subsidies for caring for the poor or uninsured.

With the state short on money, though, the administration is looking to increase the assessment.

Corbett on Thursday declined to comment specifically on Norquist's letter, but said that he views the hospital assessment as a fee, not a tax.

But it could give the more than 30 lawmakers in Pennsylvania who have also signed the pledge pause before casting a "yes" vote.

The Senate is expected to return Sunday to start the process of approving the budget and other related bills.

The House would vote on it after that.

The goal is to have a budget signed by Thursday's deadline.

Contact staff writer Angela Couloumbis at 717-787-5934 or acouloumbis@phillynews.com.