Mayor Kenney's bold initiative to revitalize the city's parks, libraries, and recreation centers as a way to fight poverty and strengthen neighborhoods is receiving a major lift - up to $100 million from the William Penn Foundation.

The grant is the largest in the foundation's history, nearly four times bigger than any it has given before. In a single swoop, it covers one-fifth of the overall cost of the program, known as Rebuild.

"We want to provide opportunity for all Philadelphia citizens, from the youngest children all the way to the most senior citizens, to come together, to get to know one another," said Janet Haas, chair of the foundation's board of directors. "Particularly in these times in our country, it's even more important."

The gift, which will be formally announced at a news conference Monday, is a significant vote of confidence from the city's largest philanthropy at a critical time in the launch of Rebuild. City officials are deep in planning the project and are expected to seek City Council approval of the first of three $100 million bonds early next year.

The program will mean improvements ranging from face-lifts to brand-new facilities at scores of parks, recreation centers, and libraries - city assets that have fallen into deep disrepair due to budget constraints.

Some parks haven't seen new equipment or substantial upkeep of the old for more than 20 years. And neighborhood libraries last received new paint, lights, and computers two decades ago. Eight branches remained closed last summer because the air-conditioning did not work.

While at a basic level Rebuild will provide for those infrastructure improvements, city officials and leaders at William Penn see the potential for a broader social and economic impact. They point to the jobs the projects will create, the increased community engagement the process will foster, and the sorely needed services that will be available at the finished facilities.

Rebuild is meant to work in tandem with expanded early childhood education, another Kenney initiative. Officials have said prekindergarten facilities could be housed in the improved facilities.

"It doesn't just rebuild rec centers," Brian Abernathy, the city's first deputy managing director, said of the effort. "It rebuilds communities. It rebuilds neighborhoods. And it rebuilds an economic base that has been lacking in this city for decades."

The six-year program has a $500 million price tag: $300 million in bonds, $120 million from foundations and private donors, $32 million in state and federal funds, and $48 million in city capital funds.

The lion's share of the William Penn grant is contingent on the city taking out bonds for its portion. About $4.8 million has already been given and is being used in the planning phases. An additional $20.2 million of the total is structured to help draw in more philanthropic and public funding, with $1 given for every $2 raised.

Shawn McCaney, the foundation's interim executive director, said the organization would help in the fund-raising. He called Rebuild an "unprecedented and once-in-a-generation opportunity" and said it could become a national model for data-driven community reinvestment, which could spur support from national donors.

Kenney praised the foundation and said Rebuild resonates with some of its core focuses including sustainability, infrastructure, and youth.

"They really believe in what we're doing," Kenney said. "And that's gratifying. And it's also energizing and it makes you want to continue to work harder."

William Penn, with about $2 billion in assets, is among the largest philanthropic organizations in the country. It is the legacy of the Haas family and was started by Otto Haas, the German-born cofounder of the Rohm & Haas chemical company, and his wife, Phoebe, in 1945.

For decades the foundation has been behind the remaking of some of Philadelphia's most significant public spaces - Logan Circle, the Delaware River Waterfront, the Schuylkill River Trail, and Dilworth Park, to name a few.

Haas said the foundation in recent years has broadened its focus outside of Center City. She said Rebuild is a natural extension of that effort.

Still, she said the decision to give such a sizable amount was difficult.

"Although we were excited about the potential, it wasn't an easy sell for the board in that we knew that it was risky and that it was going to be big," Haas said. "If we were going to take a stake in it we knew we wanted to take a big one."

She said board members asked "countless questions" to vet the project and described herself as a skeptic during the process, wanting to understand how the city would define success and the likelihood of achieving it. After going through those steps, she said, the size of the grant can be viewed as a sign of the foundation's deep confidence in the plan and the people behind it.

In weighing the final figure, Haas said she also considered other large grants the foundation has given in the past, then considered the possibility to make a citywide impact with Rebuild.

"I had a sense this would be about right," she said of the amount. "It's a stretch. You really have to hold your breath to do this. But it's the right thing to do. . . . It's out of the comfort zone. But big things always are."

With the big donation, Haas said the foundation is also anticipating a big impact and plans to remain invested in the process to help see that happen. She said she has toured many of the facilities Rebuild would revitalize and seen how they are lacking. A visit to one South Philly rec center several years ago stands out in her memory.

The facility was locked when her group arrived. After tracking down the key, Haas said, she was struck with the feeling that the building wasn't even worth locking.

"There was no point," she said. "It was vandalized on the outside. There had been a basketball hoop, but there was basically nothing left. There was a puddle on the floor, and buckets. And it hadn't just been raining."

Haas said Rebuild could remake those public spaces into vibrant community hubs. She and McCaney added that the process of doing so is, in their eyes, almost as important as the end result. City officials have said community input will be central in developing specific projects, so the new facilities fit the communities' needs.

"We used to think you use the engagement process to deliver a physical thing," McCaney said. "Now we think that it's actually the reverse. That the park is a platform for engagement. That the process leading to the park is an engagement process. And that, if you . . . do it right, folks feel like they own that space, they respect it, they steward it, and that there's ongoing engagement beyond."