WE ARE living in a time of great cultural shifts. And with the majority of the country living in metropolitan regions, and a president who knows what it is to be a city dweller, that time is destined to be good for cities like ours.

In fact, a few months back, we recognized this "metropolitan moment" as the policies and priorities of the past were being rethought and cities - with their dense infrastructure, walkable neighborhoods and energy efficiency - were finally being seen as hubs of solutions rather than of problems.

President Obama recognized this when he appointed Adolfo Carrion to head the White House Office of Urban Affairs. Today, Carrion and other members of the Obama administration are launching what they're calling a national conversation on the future of urban and metropolitan America. And that conversation kicks off right here, at a ShopRite supermarket in West Philadelphia.

The bigwigs from Washington -including Carrion, Agriculture Secretary Tom Vilsack, Commerce Secretary Gary Locke and Housing and Urban Development Deputy Secretary Ron Sims - are visiting a supermarket because it is the centerpiece of an initiative that recognizes the importance of all neighborhoods to have access to fresh foods. For too long, low-income neighborhoods have been centers for fast food and small, high- priced grocery stores, with few large supermarkets. That limited access not only to lower prices but to healthier fresh foods, like produce.

Several years ago, state Rep. Dwight Evans became an early advocate for bringing supermarkets back to urban neighborhoods, and thanks to grants he generated, big supermarkets are coming back to the city's neighborhoods, including a new ShopRite.

The fresh-food issue is also one that neatly dovetails with another big idea: urban agriculture. As Obama pointed out in a speech last week, making fresh local food supplies within a short walk for most city residents can help the economy and the environment.

And while it's ironic that the first chapter of a conversation on urban affairs has to do with agriculture, it also provides a great example of just how cities can provide innovative solutions that cut across a wide range of concerns. Fresh food can promote healthier living. Growing fresh food in urban gardens can be an economic engine, and helps with the city's sustainability goals. It can also provide a productive use for the city's inventory of vacant land.

But these wide-ranging impacts also demand that governments dissolve their bureaucracies that keep one department from ever talking with another. That's going to be a big challenge for government at all levels - federal, state and city.

Governments and their leaders are often more comfortable drawing their maps with political and geographic boundaries, rather than strategic ones. Mayor Nutter seemed to confront this when he established the Metropolitan Caucus to encourage problem-solving with the city and county commissioners. But if the big new ideas coming out of Washington and out of our cities have any hopes of changing the world, the ideas must come with a shift in mind-set.

Otherwise, the promise of Philadelphia farming will yield nothing but a good idea that might have been. *