Dozens of cities, including Detroit, Flint, Mich., and Youngstown, Ohio, have been ravaged by staggering declines in population and vast neighborhood blight. Some planners are advocating controversial "shrinking-cities" strategies aimed at demolishing thousands of derelict structures, converting blighted blocks to open space or other uses and providing incentives for residents of decrepit neighborhoods to move to healthier ones, in part to save on municipal-service costs. But critics say demolishing parts of cities is the wrong way to save them, and they point to failed urban-renewal efforts of the 1960s as evidence. Meanwhile, progress is slow in cities that are trying to remake themselves. Funds for demolition and cleanup are tight, and residents fear being forced to relocate -- a practice city officials deny advocating. Moreover, intractable urban problems such as poverty and unemployment make the prospect of reducing blight especially daunting.