An estimated 46 percent of the nation's urban population lives in a category of neighborhoods that local governments pay little attention to: America's "middle neighborhoods." These neighborhoods are generally affordable and attractive, and they offer a reasonable quality of life, but many of them are in danger of decline.

Middle neighborhoods typically receive little or no attention from mayors, city managers and local housing officials, in part because they are not distressed enough to qualify for federal Community Development Block Grant funds and because financially stressed local governments seldom allocate local tax dollars to neighborhood-improvement strategies. Yet, these neighborhoods, which provide a substantial portion of local property-tax revenues, can easily tip into decline unless steps are taken to improve the investment psychology for them.

A recently published collection of essays, "On the Edge: America's Middle Neighborhoods" (edited by one of this column's authors), provides some surprising insights into these neighborhoods. The portion of the population of the cities studied by the book's contributors living in middle neighborhoods, for example, ranges from 37 percent in Milwaukee and Pittsburgh to over 51 percent in Detroit and Baltimore. The book describes the challenges these neighborhoods face as they try to hold their market position in cities.

Demographic and economic changes are certainly among those challenges. The middle class is shrinking, and numerous scholars report that we are increasingly segregated by family income. These trends represent a real threat to middle neighborhoods, which generally are more integrated, in terms of both race and income, than either strong or distressed neighborhoods.

Another challenge is that family size and housing preferences have changed since many of the houses in middle neighborhoods were constructed, making many sections of middle neighborhoods difficult to market to today's homebuyers. This problem is exacerbated by the fact that in some metropolitan areas suburban housing -- with its perceived advantages of better schools and safer streets -- can be purchased for prices similar to those in middle neighborhoods.

Access to jobs is also a challenge for middle neighborhoods. When they were first developed, these neighborhoods were close to job centers, but as jobs have suburbanized or located in the less-dense fringes of cities, middle neighborhoods have lost proximity to employers as an attractor to newcomers.

A common theme across the essays is that while there are social benefits to stabilizing middle neighborhoods, there also are strong economic reasons to do so. Stabilizing a middle neighborhood is far less costly and more foreseeably successful than attempting to reclaim a neighborhood after the cycle of distress has devastated it.

To that end, promising efforts to improve middle neighborhoods are underway in some cities. Baltimore and Milwaukee, for example, have adopted a model that helps these neighborhoods improve through active resident involvement, strategically selected public improvements, neighborhood marketing, and participation of lenders and foundations to make mortgages and home-improvement loans available on favorable terms. While these "healthy neighborhoods programs" are run by organizations outside of city government, the support of city governments is crucial.

In other places, neighborhood-based groups are succeeding at marketing their middle neighborhoods in ways that are building demand in middle neighborhoods. And still other communities are deploying impactful preservation strategies, including appropriate financing vehicles, that improve older properties with visible maintenance issues. (To keep current on efforts like these, go to www.middleneighborhoods.org.)

Local governments' goal should be to recognize the critical importance of middle neighborhoods and invest in them, as we already do in our very distressed neighborhoods and our downtowns, so that they can continue to serve their vital and historic role in American cities. As Henry Webber, one of the "On the Edge" essay authors, writes, "Without this assistance, many middle neighborhoods will decline and cities will be increasingly challenged." The last thing our struggling cities need is another challenge.