THE future of America's large older cities depends partly on how willing they are to give up the past and take up a new role. Urban experts say that most major Midwestern and Northeastern cities will never again be the centers of population, wealth, and semiskilled jobs that they were after World War II. Their economic vitality will depend - at least for a while - on much more outside help than in years past.
But that doesn't mean they are destined to become the hole in the metropolitan doughnut.
Many urban experts are convinced that these smokestack cities do have a future. But their shape, makeup, responsibilities, and strengths are undergoing some radical changes.
As urban sprawl continues, most such cities are becoming smaller. It is a fact no mayor likes to face. Becoming a medium-size city means having a smaller tax base and less clout in winning state and federal funds.
''Most mayors want desperately to believe that it's all a mistake and that they have the power to change what's happening,'' says Charles Leven, professor of urban affairs at Washington University, over a lunch of sole at the Faculty Club.
''Their only mistake is a slavish devotion to trying to recapture a halcyon past which is just not recoverable.''
''One has to have deep sympathy for these guys,'' says Cleveland State University urbanologist David Garrison of such mayors. He likens them to managers of large corporations whose assets are deteriorating but cannot be moved for a fresh start. He counts it a significant sign of progress that managing urban decline is now an acceptable discussion topic in public forums.
The populations of these more compact residential, financial, office, and government centers in the frost belt are increasingly lower income, less skilled , and more minority. Some neighborhoods are becoming more racially mixed in response to determined citizen efforts. But residential segregation in many industrial cities remains noticeably strong. Cleveland's East Side, St. Louis's North Side, and Chicago's South and West sides, for instance, are predominantly black.
If middle-income whites are to be encouraged to stay in the city or move back from the suburbs, a more energetic effort must be made to break the ''self-fulfilling prophecy of ghettoization,'' insists University of Chicago political scientist Gary Orfield.
''It's a problem we're capable of solving collectively, but not by talking around the edges of it.''
A few large industrial cities now have black mayors. Longtime Detroit Mayor Coleman Young, who won a voter-approved payroll-tax hike and city worker wage concessions during a financial crisis a few years back, has successfully integrated much of the city's work force and linked local development with stepped-up minority hiring.
But National Urban Coalition president Carl Holman says blacks tend to get the top job only when cities are almost past saving. More blacks, he says, should also run for state and suburban offices that still control much of what happens to cities.
Most industrial cities have been working hard to diversify their job bases. In Pittsburgh, for instance, where the steel industry has been cutting jobs for the last 20 years, the University of Pittsburgh is now the No. 1 employer.
''This is no longer a steel town,'' insists United Steelworkers of America spokesman Gary Hubbard at union headquarters. One of the hottest local disputes, he adds, is whether to turn an old Jones & Laughlin mill into a jail annex or a museum.
And Baltimore, trying to build on its strength as a hospital center, now claims an even mix of government, service-sector, and manufacturing employees. ''Employment levels have stayed the same, but the composition has changed,'' says Bernard Berkowitz of the Baltimore Economic Development Corporation.
That kind of success in stemming losses prompts Donald Haider, a professor with Northwestern University's Kellogg School of Management, to rate Baltimore as the most successful in economic development of any of the major industrial cities.
''My guess is that Baltimore would have lost a lot more jobs, had far less economic activity, and less sense of its future and identity if it hadn't done what it did,'' he says.
''I'm not talking about a Renaissance but relative stability. . . . I don't think you're going to see a Gary, Ind., for instance, rising Phoenix-like from the ashes,'' Professor Haider explains. ''But you might be able to do some things at the margin that will help it stabilize and have economic activity without total dependency on manufacturing.''
Haider also credits the leaders of many industrial cities with a new ''sobriety'' in assessing their cities' strong and weak points and in no longer assuming that the downtown shopping center, the domed stadium, or the high-tech park will save the day. ''There is no single panacea,'' he says.
Federal policies often make a large difference. It is widely agreed, for instance, that the building of Interstate highways through cities and the availability of tax credits to homeowners encouraged the suburban exodus. But now that large industrial cities are at a strong disadvantage in the competition for new jobs, urban experts say the city impact of development policies must be more carefully thought through.
''Should federal and state tax funds subsidize removal of low-income jobs from central cities already collapsing to places where it's impossible for the poor to live or have access?'' asks Chicago's Dr. Orfield.
Some contend that welfare, job training, and housing policies must also be rethought with an eye to the social effects they help produce. The National Urban League's 1984 report notes that 83 percent of all black children are born to unwed teen-age mothers. Other studies indicate that few of the young mothers get back into high school or have any contact with those who have jobs, go to college, or get married.
''If nothing is done, we're just creating a whole separate culture,'' Orfield insists.
Robert C. Embry Jr., former assistant secretary of Housing and Urban Development (HUD), suggests that the US may be the only developed country in the world which in effect ''blesses'' an event that used to be censured by giving unwed mothers a welfare check.
''I'm not saying they have children to get the money, . . . but the whole structure of our society is set up in a way which encourages what is happening.''
Roosevelt University urbanologist Pierre deVise suggests that the US could take some cues from the European practice of group day care, in which some mothers tend the children while others take paying jobs.
''In Chicago we'd have the setting for something like this with public housing, where 90 percent of the families are headed by women. But it would be so contrary to middle-class values that it probably wouldn't have a chance,'' he says.
The Reagan administration's largely hands-off policy on cities calls for $9.2 billion more in domestic spending cuts in next year's budget. But in response to strong mayoral insistence, it does continue urban- and community-development grants.
It is generally agreed that the administration's proposed enterprise-zone legislation, aimed at helping distressed urban areas draw new business and jobs by tax incentives, is worth a try. But many urban experts say they doubt it will work without the additional stimulus of seed money.
''The administration offers no carrot,'' says Roger S. Ahlbrandt Jr., a former HUD deputy assistant secretary in the Reagan administration's early days.
There is widespread skepticism that the new Job Training Partnership Act will make much of a dent on the double-digit employment that prevails in many large industrial cities.
''It's cleverly written,'' but the way it's structured will cause only the most able job candidates to be trained, says Lois Work of the urban coalition New Detroit.
But most distressing of all to those who care about cities is the apparent general lack of interest in the subject in 1984. They argue that presidential candidates in both parties, for instance, perhaps echoing a lack of concern among voters at large, have had little to say on urban issues. ''There's very little discussion of what our policy ought to be,'' says Embry.
''When you say cities,'' adds the Urban Coalition's Mr. Holman, ''people think of blacks, Hispanics, and poor, but it's a vital part of leadership to make it clear why it's important to focus on this. . . . I can't believe we're going to permit the continued deterioration of our cities.''