What factors have made American cities into what they are during the past half century? And what will those factors be in the next 50 years?

Here are some developments that shaped cities in the past, according to a survey of 149 leading urban planners, historians and architects sponsored by the Fannie Mae Foundation:

• Interstate highways and the dominance of the automobile, federal mortgage financing and subdivision regulation, de- industrialization of central cities and urban renewal.

• Also, mass-produced suburban tract homes, racial segregation and job discrimination, and enclosed shopping malls.

• Finally, Sunbelt-style sprawl, air conditioning and the urban riots of the 1960s.

What awaits U.S. metropolises in the next 50 years?

• Analysts say metropolitan areas will be shaped by growing disparities of wealth, growing political clout of suburbs, aging of the baby boomers, and a perpetual "underclass" in central and close-in suburbs.

• Regulations and plans to limit urban sprawl, the Internet, deterioration of close-in suburbs, and shrinking household size.

• Finally, expanding superhighway systems to serve new cities on the edges of old cities, and racial integration.

The survey was conducted by Robert Fishman, of Rutgers University and the Woodrow Wilson International Center for Scholars.

Source: Haya El Nasser, "Urban Experts Pick Top Factors Influencing Future," USA Today, September 27, 1999.