One by one, the totems of poverty that once dotted Philadelphia's urban landscape have been disappearing. Since the late '90s, the Philadelphia Housing Authority has imploded 23 public housing towers and replaced them with traditional rowhouses. On March 19, two more of those alien towers, the Norman Blumberg Apartments, will be reduced to dust in the North Philadelphia neighborhood the PHA has dubbed Sharswood.

This time, however, the housing authority's ambitions are much bigger than usual. Rather than limiting itself to installing PHA rowhouses on the cleared site, the agency has concocted a grand plan to take over the neighborhood that surrounds the towers - a vast band of territory between Girard and Cecil B. Moore from 19th to 27th Streets. The PHA says its goal is to remake the area from the ground up as a model community of affordable housing, complete with a reinvigorated commercial strip on Ridge Avenue.

If this sounds a little like the failed, old-style urban renewal in new clothes, well, it is.

PHA is in the lengthy process of seizing 800 private parcels through eminent domain - many of them vacant lots - and will acquire 500 more from public owners. What makes the authority think it can get things right this time?

Unlike the urban renewal of the '50s and '60s, which was meant to revive neighborhoods that had no hope of private investment, the Sharswood project is a response to Philadelphia's growing concerns with gentrification. Because Sharswood is sandwiched between the rapidly changing Brewerytown and Francisville neighborhoods, and the expanding student zones of Temple University, it now sits in the direct path of development. PHA's goal is to preserve Sharswood as an oasis of affordability before the deluge hits.

There's a definite logic in that approach. Sharswood is one of the most devastated neighborhoods in the city, and the high concentration of empty lots means there is plenty of unwanted land for affordable housing. The problem is that PHA's target area also encompasses remarkably intact blocks where homeowners have stuck it out for years.

You can see remnants of the surviving community on homey blocks like the 2300 block of Nicholas Street, with its Flemish-gabled houses, or in the small churches that tremble with music on Sunday mornings, or in the community garden known as the North Philly Peace Park on Jefferson Street. Jacquelyn Courtney, a third-generation resident widely known as Miss Jackie, has organized a "Friends and Family" day on Turner Street for years. Adam Lang, a more recent arrival, hosts movie nights for his neighbors in his sideyard on Master Street - a yard that PHA is now trying to seize through eminent domain.

Could Sharswood use some emergency care? Absolutely. Is PHA the right agency to resuscitate the struggling neighborhood? Some redevelopment specialists worry about the authority's ability to take on a job that isn't just about housing.

The agency, they say, knows nothing about commercial redevelopment, urban design, placemaking, or preservation - all skills essential to the revival of any shattered neighborhood. PHA is also just emerging from years of turmoil under two disgraced leaders.

"I am intrigued by the boldness of this plan, but I worry about the mismatch of ambition and capacity," said Jeffrey Allegretti, a former city official who now specializes in developing subsidized housing. "PHA is set up to provide public housing but is now unilaterally implementing a grand reenvisioning of this part of the city. It highlights the problem of PHA operating outside of the city's planning and development purview."

Reviving Sharswood's Ridge Avenue as a shopping street is key to the project's success, but its previous attempt at retail, on the East Falls section of Ridge Avenue, was a failure. A decade after it completed a new housing project there, most of the shops remain unrented.

Just as worrisome is the lack of detailed design guidelines in PHA's master plan. To attract retailers to Ridge Avenue, the agency is preparing to relocate its headquarters from 23rd and Market to Sharswood, to serve as an anchor.

Yet the six-story office building, set to begin construction later this year, has no retail planned for the ground floor and will be surrounded by surface parking. PHA's president, Kelvin Jeremiah, told me that the parking lot on Ridge is only temporary until retailers can be signed, and that he was committed to maintaining the corridor's urban form.

In recent years, PHA has done its best work on the tabula rasa sites it created after demolishing high-rise towers. But critics say the agency is less adept at managing infill projects in existing neighborhoods. That's the kind of sensitive development that Sharswood's gap-toothed, 19th-century blocks need.

As Philadelphia's largest property owner, with more than 4,400 scattered sites around the city, PHA has often seemed indifferent to such older buildings. Many of the tumbledown houses and vacant lots that contributed to Sharswood's blight have been owned for decades by the PHA.

A recent study undertaken by a group of historic-preservation students at PennDesign, led by architect Fon Wang, raised alarms about the agency's lack of attention to preservation in Sharswood.

Although the first three phases of the 10-phase project are underway, the agency is only just beginning to inventory the area's important structures, which include old jazz clubs, a house where Malcolm X lived at 25th and Oxford, and dozens of houses decorated with turrets and stone carvings. The students fear the agency will acquire significant historic buildings through eminent domain only to allow them to sit empty for years. Jeremiah said he shared their preservation concerns and was working to identify good infill sites.

A harder problem will be the cost of the new housing, which will be a mix of 1,200 rentals and sale properties. Because PHA is obliged to use union labor, each new house will cost $400,000 to build. Those put up for sale will probably have to be subsidized to the tune of $200,000, PHA acknowledged.

That seems like a crazy way to spend scarce housing dollars. Malik Carter, a former PHA property manager who left the agency to renovate houses, told me he was now selling rehabbed shells for as little as $150,000. "There are lots of places around the city where you can buy a house for $200,000 and not be in the middle of an experiment," Carter added.

PHA's first 57 houses are under construction across from the Blumberg towers. In appearance, the cozy, three-story houses are clearly a big improvement over the weedy lots that were there only a few weeks ago. Now PHA just has to figure out how to build the next 1,143 units.