The Nutter administration has developed a plan to convert its huge holdings of vacant lots and asphalt-covered school yards into tree-shaded greens, in a low-cost effort to satisfy a 2009 pledge to add 500 acres of parkland.

The kinds of parks envisioned in the ambitious Green2015 plan, which will be released Tuesday, would be very different from a traditional city park like Rittenhouse Square or Forbidden Drive. Instead of building a few large destinations for recreation, the city would establish an archipelago of green oases on scraps of land, some as small as a quarter acre.

Like many of the Nutter administration's recent initiatives - from the crosstown bike lanes to the new riverfront paths - this one bears out the governmental philosophy that cities can still make public improvements in hard times, but only if they do so incrementally and can get others to pay for them.

So an entire section of the report, prepared by the nonprofit consultant PennPraxis, is devoted to identifying federal and private agencies that provide grants for urban greening.

The report enthusiastically notes that Philadelphia International Airport will be required to replace 82 acres of lost wetlands if a planned $5.3 billion runway expansion goes ahead. Private owners, mainly institutions, will also be enlisted in the greening effort and encouraged to replace surface lots with trees and grass.

"It's a doable plan in a difficult economic time," said Michael DiBernardinis, commissioner of the city's Parks and Recreation Department, which sponsored the report, obtained by The Inquirer.

Within five years, he predicted, the proposals would "reshape the physicality of the city" by softening old factory neighborhoods where greenery is in short supply. It costs about $250,000 to create a one-acre passive park, the report estimates.

The plan's strategy is purposely structured to allow the city to tackle a variety of other urban problems simultaneously. By distributing pocket parks around the city, Green2015 could help Philadelphia provide more play space in underserved neighborhoods, combat childhood obesity by creating exercise space, reduce polluting water runoff reaching the city's rivers, raise property values, and attract new development.

Nutter's earlier Greenworks, in 2009, garnered the city national attention for its ambitious goals.

Nutter will release the report Tuesday morning at North Philadelphia's Gathers Recreation Center, the first on the report's list of rec centers to be greened.

In the evening, the city will hold a public presentation at the Academy of Natural Sciences, starting at 6 p.m. Although 600 people have signed up for the event, a small number of free seats may be available on a first-come basis.

PennPraxis director Harris Steinberg, who prepared the report, explained that Green2015 intentionally relies on a shop-your-closet philosophy because Philadelphia has so little money to invest in public amenities. Almost no land would be purchased to meet Nutter's 500-acre goal. The report includes a priority list of city-owned, ready-to-green spaces.

The consultants recommend that the Nutter administration start by breaking up unused concrete and asphalt at the city's schools and rec centers, since they are already a convenient draw for neighborhood children.

Unlike newer, suburban facilities, many of Philadelphia's schools and rec centers have no green space at all. One of the plan's main goals is to ensure that every city resident has a green park within a 10-minute walk, or a half mile. Currently, the report estimates, 200,000 Philadelphians lack such convenient access despite the fact that the city boasts one of the largest park systems in the country - the 9,995-acre Fairmount Park system.

"We've always talked about how much parkland we have in Philadelphia, but the problem is that it is all in one place," said Shawn D. McCaney, a program director at the William Penn Foundation, which helped fund Green2015.

The plan also targets other areas ripe for greening, such as vacant lots, abandoned railroad rights-of-way, waste ground below elevated highways, and the banks of neglected streams. Several much-discussed projects, including the Reading Viaduct in the Loft District and the Logan triangle off Roosevelt Boulevard, are high on the list of greening projects.

Green2015 is as much about managing stormwater runoff as it is about creating parks. The Philadelphia Water Department has its own plan, called Green City, Clean Waters, which lays out a strategy for replacing asphalt and concrete - including some city streets - with planted and porous surfaces. The department hopes to cut runoff pollution in half by 2030, Deputy Commissioner Howard M. Neukrug said.

Part of what makes Nutter's 500-acre goal obtainable is the accounting method for tallying new park space.

The report estimates that 100 acres have already been greened through existing programs, such as the Pennsylvania Horticulture Society's Clean-and-Green effort, which has been planting abandoned lots with grass since the days of the Street administration. Several public schools, such as Greenfield in Center City, have recently raised money on their own to soften their play areas.

The report makes no provision in its accounting for subtracting naturally green land lost to asphalt as a result of new construction, such as the recently completed SugarHouse Casino.

That project covered the better part of its 21-acre site with a surface parking lot, although it did provide the public with a generous waterfront path. And while the airport may fund 82 new green acres, it plans to fill in the equivalent amount of wetlands.

In the future, some of the 500 acres planned under Green2015 won't be visibly green at all. Because the city is as interested in controlling runoff as in building new playgrounds, some ordinary asphalt lots will be repaved with porous asphalt, a product that absorbs rainwater much like a lawn.

The city may eventually use porous asphalt for all of its streets.

As Steinberg noted, the city should be able to divert some of the $21 million it now spends each year to maintain vacant lots to creating passive green space.

The plan also calls for the city to step up efforts to train volunteers to handle maintenance and tree-planting at the new mini-parks.

But, as a backup, it advises the city to design the spaces to be as self-sustaining as possible, with no-mow plants such as buffalo grass.