The mayor said students are not responsible for the funding problems, and "they should not suffer as we try to resolve it."
"They should not be pawns in a political chess match of leverage and strategy," he said.
Nutter's announcement came the day before a fiscal deadline set by the head of the struggling district.
Superintendent William Hite said he needed a $50 million commitment from city or state officials by Friday in order to ensure sufficient school staffing on Sept. 9.
On Thursday, Hite said the mayor's monetary pledge "will enable us to provide many crucial school functions and restore critical staff positions," as well as keep class sizes down.
Gov. Tom Corbett urged the council to authorize the $50 million in borrowing. The state has overseen the Philadelphia district since 2001.
But shortly after Nutter's news conference, City Council members expressed strong opposition to a loan. Earlier this week, they sent Hite their own proposal to generate the needed funds through the sale of surplus school buildings.
Hite did not mention that plan in his statement. District officials have said that such real estate transactions are already included in their five-year budget, and that council's proposal would not represent new revenue.
Council President Darrell Clarke said members believe the property is worth about $200 million, far above what the district has budgeted. And he maintained that Nutter can't borrow money without council approval.
So while the actual mechanism for delivering the emergency funds still appears to be in flux, a district spokesman said both plans met Hite's demand for a financial commitment by Friday.
"We have two assurances that the city will work out an arrangement to provide the district with $50 million," spokesman Fernando Gallard said.
The district is now expected to hire back about 1,000 workers, from assistant principals to lunchroom aides. They are among 3,800 employees laid off this summer to close a $304 million deficit.
Yet even their rehiring is fraught with controversy. Hite got approval late Thursday from the School Reform Commission, which oversees the district, to bypass seniority in recalling staff. Such flexibility will allow employees to return to the buildings where they worked, he said.
Teachers union president Jerry Jordan contends such a move violates their contract, and he said the group is looking at all legal options. Getting rid of seniority will lead to patronage hires, he warned.
Meanwhile, some education advocates say even the $50 million infusion is not enough. On Monday, a group of concerned clergy asked parents to consider keeping their children out of school unless the district gets more funding.
Hite originally asked the city for $60 million, the state for $120 million and the unions for $133 million in givebacks. He has urged City Council to direct revenue from Philadelphia's sales tax to the schools, but Clarke wants some of that money for the underfunded city pension system.