WHAT'S ahead for the proud cities that were once the backbone of industrial America? In recent years these large older cities of the Midwest and Northeast have been pushed and pulled by strong economic and population forces that have left parts of them looking like bombed-out war zones. Anyone driving through Chicago's West Side, New York's South Bronx, or down Detroit's once riot-torn Rosa Parks Boulevard sees ample evidence.
In part, it's a reflection of the big-city exodus to the suburbs and Sunbelt that's been going on for years. Those with more job skills and the means to leave have been the movers. Increasingly, the jobs have moved with them. Over the last two decades, for instance, Chicago lost almost 100,000 jobs, while its surrounding suburbs gained six times as many.
The central cities of what is now often called the ''rust belt'' - as the United States shifts from a strong manufacturing emphasis to a more service-based economy - are increasingly poorer, blacker, and smaller.
Of the seven cities visited by this reporter in the course of this series - Baltimore, Pittsburgh, Cleveland, Detroit, Indianapolis, Chicago, and St. Louis - all but Indianapolis hit their population peaks in 1950. St. Louis, for instance, once the nation's fourth-largest city and now 25th, has lost close to half its residents over the last three and a half decades. In Detroit, now 63 percent black, 30 percent of all city dwellers live below the poverty line - a 7 percent hike just since 1980, according to the latest Census Bureau data.
Since Southern blacks began flocking to Northern cities during World War II, when manufacturing jobs were plentiful, the nation's black population has become increasingly urbanized. Seventy-five percent of all blacks now live in cities. Currently close to half of all black households are headed by women. A high percentage of working-age black men are unemployed.
''Over the last two decades, distressed cities have even become more distressed,'' says Robert C. Embry Jr., a former assistant secretary of the US Department of Housing and Urban Development under President Carter and now a private developer in Baltimore. ''The poor population has increased, and the situation of the poor has grown worse.''
Mr. Embry says he is particularly concerned about the departure from cities of large numbers of middle-class blacks, who are often churchgoers and put a high premium on education, hard work, upholding the law, and having children only after marriage.
Their presence in cities and strong endorsement of that value system, he argues, have long served as important models for other city dwellers farther down on the poverty scale.
Roosevelt University urbanologist Pierre deVise estimates that as many as one-fourth of those living in major cities really shouldn't live there and often don't want to. ''They're people who are dependent and unable to work. But the institutions to help them - from public housing to welfare - are there, and it is hard to leave.''
For many of these older industrial cities, crime, poor schools, and decaying infrastructure are increasingly serious problems. Yet federal cutbacks and a shrinking local tax base make it harder than ever to finance improvements.
Some economists and demographers argue that the forces of urban decline now at work in these cities are self-reinforcing and virtually irreversible. They note that the exodus of jobs and middle-class residents continues - though at a somewhat lesser rate - despite all-out local efforts to encourage businesses to start or expand within city limits and to lure suburbanites to buy city homes.
''Right at the moment the immigration back in is only a trickle,'' observes George D. Wendel, director of the Center for Urban Programs at St. Louis University. ''The developer tends to see that as the forerunner of a flood. The social scientist is inclined to say, 'Show me the flood when it gets here.' ''
In recent years two major studies on urban decline - one by the Brookings Institution and one directed by Richard Nathan, head of Princeton University's Urban Research Center - concluded that positive efforts to rebuild the nation's older cities have not kept pace with the decay and that the situation is unlikely to be reversed anytime soon.
Still, there are many urban dwellers in these United States who are fiercely pro-city - relishing the camaraderie and adventure as well as the many cultural and recreational assets - who are unwilling to accept such a verdict. They say the adverse trends are not set in concrete and that a Renaissance of sorts is under way.
With enough support and imagination, they say, it can make a significant difference.
''It's going to take unremitting guerrilla warfare - you just have to keep plugging away,'' cautions Melvin Levin of the University of Maryland's School of Social Work.
There are some encouraging economic and demographic signs.
The general aging of the population, for instance, means fewer urban residents in the high-crime teen years and should mean less competition for jobs among those of working age. Recent studies also suggest that many who grow up in poverty are not necessarily locked into it as adults.
Although three of the rust-belt cities - New York, Cleveland, and Detroit - have faced serious financial trouble in the last 10 years, all have escaped bankruptcy. New York, in dire straits in 1975 and a city that has now largely shifted its job base away from manufacturing, expects to end the year with a $ 200 million surplus.
There are visible signs in some cities of the recovery now under way. In Detroit, the parking lots of auto assembly plants are filling up again, and the auto production count on signs over city freeways increases every few seconds.
The downtown core of almost every major industrial city is undergoing a significant construction boom. Sometimes, as with Cleveland's renovated Arcade Building - an indoor shopping mall with live music that has become a popular luncheon spot - a fresh start with an old building makes the difference.
Most cities are also working hard to improve local housing options and recruit every possible tourist and convention.
Helping in all this is an almost tangible new spirit of cooperation and determination to meet the urban challenge.
''We've raised more money and provided more services to the commmunity since Reagan became President than at any time in the 141/2 years I've been here,'' insists the Rev. James Hannah, pastor of Cleveland's Central Christian Church and head of the Inner-City Renewal Society there.
''When black people are laid off and jobs are few, they have a tendency to come back to the church.''
''Most of the successful efforts in community renewal are led by people who are going to continue living in these cities - they're essentially survivors, and they are making progress,'' says Ken Allen of Volunteer: The National Center for Citizen Involvement.
Still, there is a growing consensus among urban analysts these days that the older industrial cities are changing in major ways that will force them to play a new role on the national scene.
Just between 1980 and 1982, for instance, Chicago slipped from the nation's second-largest to third-largest city, while Detroit led the nation with a record 5.3 percent population loss, according to new census data.
''The demographic forces that have begun to empty these cities out are huge and can't be changed in fundamental ways,'' says David F. Garrison of Cleveland State University's Urban Center. ''The challenge for the leadership in these cities is to recognize these forces for what they are and try to bend them a little but not to spend a lot of time wringing their hands.''
While industrial production and employment are unlikely to reach peak 1979 levels again, manufacturing will remain the region's economic mainstay.
''We need to think about rebuilding the industry we have left to make it more competitive - high-tech is not going to be the salvation of this region,'' says Vijay Singh, director of the University of Pittsburgh's Center for Urban and Social Research.
But forecasters say the growth in service jobs in the rust belt over the next decade will not match the decline in manufacturing jobs. Numerous studies, including one by the Federal Reserve Bank of Chicago, say years of difficult regional adjustment lie ahead.
Anthony Downs, a senior fellow at the Brookings Institution and one of the authors of its study entitled ''Urban Decline and the Future of American Cities, '' says the real-wage advantage Midwestern auto and steel workers have had over most of the nation's other industrial workers is going to have to come down if the region is to regain its economic viability. ''It's hard to get people to give up what they've got, but it seems to me the Midwest in particular is in for an adjustment period.''
Chase Econometrics vice-president Lawrence M. Horwitz suggests that such evening out of regional differences is already under way. He points to the recent shutdowns of General Motors and Ford plants in California (presumably because of the high cost of shipping parts from the Midwest) and the willingness of foreign-car manufacturers to locate in more traditional high-wage areas - such as Honda in Ohio and Nissan in Tennessee - as signs.Next: Cities woo business back, but neighborhoods want a share of the development pie, too