In 2004, Sister Mary Scullion wrote a letter to the Philadelphia Housing Authority, asking for help. Could her nonprofit acquire two of the agency's boarded-up homes in the 2100 block of North 28th Street?

Empty for years, the North Philadelphia houses would be part of a block-wide project to fix vacant homes for resale to low-income families.

For seven years, Project HOME, which helps homeless people with services and housing, waited for a decision.

And waited.

"We never knew where we stood with PHA," Scullion said.

Now she does.

In an about-face noted by many groups in the city that develop affordable housing, PHA has put out the welcome mat, asking whether they could use any of the properties in the agency's vast inventory of vacant land.

PHA owns about 3,300 vacant houses and lots and last year got approval from the federal housing agency to dispose of about a third of them.

Michael P. Kelly, PHA's new administrator, said the authority wanted to make better use of its idle property and work with others to improve blocks where a boarded-up PHA house may stand out like a "broken tooth."

"Philadelphia is a city with a great track record of nonprofit capacity for rebuilding neighborhoods," Kelly said.

In addition to reaching out to nonprofit developers, Kelly said PHA would sell houses or lots to the public at the market rate. In a month or so, it will post the locations of 1,275 available properties on a vacant-land website maintained by the Redevelopment Authority.

"Clearly, the nonprofit development community is more closely linked to our mission and the folks we want to serve, but that's not to say the private sector can't participate as well," he said.

PHA is still working out the details. Among those is a requirement for a "reverter provision," aimed at preventing speculators from buying and holding land, or trying to quickly "flip" properties for profit, Kelly said. In other words, "If you're doing the wrong thing, we can take back the property," he said.

Ed Covington, the RDA's executive director, said including PHA's properties on a consolidated city list was "more than a symbolic move."

He said it marked an important step for coordinating how the city manages vacant land. City agencies and PHA account for a third of Philadelphia's 40,000 vacant properties, according to data compiled last year by Econsult Corp.

"I could dance over this," said Bridget Collins, a city deputy managing director who works on vacant-land issues.

Mayor Nutter has made combating blight a priority. But until now, PHA has been missing from the table in discussions about the problem. Kelly now participates in all high-level discussions about the city's vacant-land surplus.

City officials and nonprofit builders credit Kelly with creating a more responsive, transparent, and cooperative atmosphere at PHA.

"This isn't just about doing someone a favor," said Nora Lichtash, executive director of the nonprofit Women's Community Revitalization Project, which helps low-income families in North Philadelphia. "This is about systematic change in how PHA deals with blight and the need for the creation of more affordable housing."

Kelly took over PHA in December after Carl R. Greene was fired over the revelation that the authority had settled three sexual-harassment complaints against him for $684,000.

One nonprofit developer, Stephen Kaufman of Community Ventures, has likened the new attitude at PHA to "the Berlin Wall coming down."

Many felt that Greene viewed nonprofit developers as competitors for public and private funding rather than partners. PHA "did its own thing, and the city was doing its own separate thing without sufficient coordination," said Rick Sauer, executive director of the Philadelphia Association of Community Development Corps.

When Kelly took office, Sauer immediately reached out to him about making vacant properties available to nonprofit builders. In April, 14 community groups submitted to PHA a wish list of 350 properties they wanted to acquire, many in North and West Philadelphia.

Many hope to acquire properties for almost nothing - transactions that will have to be approved on an individual basis by the U.S. Department of Housing and Urban Development, which could take considerable time.

The Northwest Philadelphia Interfaith Hospitality Network, which helps homeless families, has asked for a single empty rowhouse in the 6500 block of North Woodstock Street in the city's Ogontz section.

Rachel Falkove, the group's executive director, said she pounced on the opportunity to put in a request. If the nonprofit could get the property for a nominal sum, it could fix up the house using volunteers and lease it to a working family for about $450 a month, she said.

PHA initially approached HUD in 2007 about disposing of more than a third of its scattered sites. The request was unprecedented: No other housing authority in the nation owns as many free-standing properties as Philadelphia.

Of its inventory of scattered sites, PHA has 5,700 houses - 4,000 of which are occupied - plus 1,600 vacant lots. Many were acquired during tough economic times in the 1960s and '70s. Properties whose owners were delinquent on taxes or that had been foreclosed on by banks were transferred or sold to PHA.

Many are more than 100 years old and costly to renovate - like the crumbling rowhouse in the 4200 block of Stiles Street in West Philadelphia that Habitat for Humanity would like to restore.

Habitat already has built nine houses on the street. If it could take control of two boarded-up PHA houses on the block, it could "tip the block in the right direction," said Jon Musselman, director of project planning for Habitat.

Habitat has submitted a plan and budget for renovating the houses. Musselman said the next step would be to inspect the properties with PHA officials and get an appraisal.

Before, he said, "it seemed the only way we could get a response [from PHA] was by going through a City Council member, but even then it didn't seem PHA was very responsive."

Now, he said, "there's a process that's clear."