As the name implies, the Philadelphia Housing Authority's speciality is housing. Though its designs have been a mixed bag - from the dystopian Schuylkill Falls towers to the gentle, rowhouse-scale MLK houses - the agency has ensured that thousands of low-income families have a basic roof over their heads. It might surprise some to learn that PHA is the city's biggest residential developer, the landlord for about 81,000 people.

What PHA does not do well is all the other things that make a Philadelphia neighborhood successful - shops, offices, schools, parks, and playgrounds. Yet that lack of expertise did not deter the agency last year from appointing itself the master developer for a vast swath of North Philadelphia between Cecil B. Moore and Girard Avenues, an area it has dubbed Sharswood. Along with building 1,200 homes and creating a community from whole cloth, PHA has pledged to restore a battered stretch of Ridge Avenue as the neighborhood's main shopping street.

It's a daunting task. Ridge Avenue never recovered from the 1964 riots, and its remaining retail is virtually on life support. PHA does bring one advantage to the game: It plans to put its new headquarters on Ridge and use it as an anchor to attract shoppers and new businesses. The presence of PHA's 400 employees, as well as a steady stream of visitors, helped persuade discount grocer Sav-A-Lot to put a store on the next block.

PHA has finally released detailed plans for the area, and, sadly, they confirm the worst fears about its overreaching. Instead of using its extensive land holdings to establish a dense business core - similar to, say, Passyunk Avenue in South Philadelphia - the agency brings a suburban mentality to the street.

The office design, by BLT Architects, was roundly rejected this week by the city's Civic Design Review board. One member, Cecil Baker, said it looked like something "you would find in Cherry Hill."

It's true the five-story PHA office building is rather bland architecture. It manages to appear big and bureaucratic without imparting any sense that there is a grand civic mission going on inside.

But it is far from a bad building, and the focus on the design's flaws misses the larger issue: PHA's plan for reviving Ridge Avenue has too much open space and too few buildings. You can't create a walkable shopping street by dribbling out the retail destinations one per block.

PHA has come a long way in understanding how cities work since its towers-in-a-park days. The 57 rowhouses going up on the site of Sharswood's former Blumberg Towers are better than anything the agency has ever built.

Designed by Kitchen & Associates, the homes hit the sweet spot between modern and traditional. Faced in good-quality brick, they are arranged in tight formation along the street, exactly the way Philadelphia rowhouses should be. Given PHA's propensity to squander land, even in good developments like MLK Houses at 13th and Fitzwater, I was especially impressed to see that the agency has finally mastered the art of infill and managed to retain some of the surviving 19th-century houses.

So why hasn't the agency applied the same disciplined urbanist thinking to Ridge Avenue?

PHA starts off on the right foot. Like its houses, the five-story headquarters at Ridge and Jefferson will form a strong edge along the street, with the main entrance facing Ridge. Even though the upper floors will be faced in that inscrutable blue glass that has become ubiquitous in all Philadelphia office buildings, BLT has managed to introduce tan terra cotta panels to provide texture and break down the scale of the large structure. PHA has even set aside two lots in the corners of the building for retail.

Yet that little oasis of density will be surrounded by a whole lot of vaguely defined, poorly designed open space. Two plazas are supposed to bookend the headquarters building. The main one, a triangular space at the Jefferson corner, will bleed into another plaza across the street, on the block where the Sav-A-Lot will be.

Part of the problem is that PHA's plan treats the Ridge Avenue diagonal as just another straight street in the city grid. That approach leaves several other triangular parcels stranded in the middle of the commercial corridor. They have been earmarked as "open space," which means they'll end up collecting trash.

Then there are the two sprawling parking lots behind the supermarket and PHA's headquarters. Altogether, the amount of land devoted to plazas and unprogrammed open space is enormous. Couldn't PHA have at least found room for a playground amid all this throwaway land?

PHA hasn't released a design for the Sav-A-Lot, but the description doesn't sound good. The one-story supermarket is supposed to front Ridge Avenue, but PHA vice president Michael Johns acknowledged the facade will probably be a blank wall gussied up with murals. Even with a second, smaller store on the block, that still leaves a lot of empty frontage.

Why is PHA even encouraging these stand-alone stores on an urban street like Ridge Avenue? It would be better for the street to make the supermarket a tenant in a larger, mixed-use apartment building. Having people living on Ridge Avenue would provide the 24/7 activity needed to support the ground-floor retail.

This suburban approach to land use would be bad enough, but when coupled with PHA's abysmal record on retail, Ridge Avenue is a disaster in the making.

Take PHA's Schuylkill Falls project in East Falls. After replacing the nightmarish towers with a mix of mid-rise apartments and twins in 2004, PHA promised to revive the shopping district with new retail. A decade later, only a single store lot in its development is occupied.

In an interview, Johns blamed PHA residents for vetoing several prospective tenants. But Gina Snyder, head of the East Falls Development Corp., says PHA's bureaucratic culture and financial constraints make it ill-suited for retail development.

Her group repeatedly tried to play matchmaker to help PHA lease the retail. "We had a great tenant who negotiated for about a year for the space," she recalled in an email. "PHA had at least three sets of outside counsel negotiating a lease for about 1,000 square feet of retail!" Eventually, she wrote, "the tenant gave up."

It's not too late to fix this mess. PHA is required to present a revised headquarters design to the Design Review Board before it can break ground. PHA's executives should use the delay to make a trip to Passyunk Avenue. A diagonal retail corridor with some resemblance to Ridge Avenue, it was revived by a nonprofit development group specializing in retail and public space. Once they see it, the lesson should be clear: Leave Ridge Avenue to the experts.