The urban riots will begin next summer. They will be worse than those of the 1960s, both in property damage and in personal injury, and they will be brutally put down.

This is not a warning from a civil rights leader hoping to pressure the government into doing something. It isn't somebody's idea of a political threat, or even an attempt to increase law enforcement outlays. It is a cool, dispassionate prediction from an international firm whose expertise is economic forecasts. BERI Ltd., a Swiss-based firm with an office in nearby Hyattsville, supplies what its name suggests: Business Environment Risk Information. It sells to its 500 or so subscribers (fewer than half of them in North America) its 48-country assessment of risks to profitability: credit restrictions, impediments to currency conversion, labor-force militancy, government instability or corruption and socioeconomic problems.

Regarding that last, BERI sees "a high probability" of riots next year, for reasons that are chilling both for their logic and for the calm way they are presented. The firm predicts that there will be a modest economic recovery in the United States by early next year. "Independent of that recovery, however, is the high probability that the permanent urban underclass will erupt in violent demonstrations during the summer of 1983, with many casualties and extensive property damage," BERI tells its $775-a-year subscribers. "These uprisings are most likely to occur in areas that are expanding rapidly with high-technology industries. The unemployable will be frustrated by their exclusion from this economy and by the cutbacks in social programs, reinforcing their sense of hopelessness. Because of the concentration of minority groups in the center- cities, the riots will be racially motivated, with blacks and Hispanics expanding gang warfare against each other as well as the establishment."

Mary McCarthy, BERI's vice president for research, doesn't suggest how this unhappy prospect might be avoided. Her task is to alert subscribers to what is likely to occur, so that they can take it into account in their investments. But she does offer a reasoned account of how we managed to fall into this socioeconomic fix. American cities have spawned a large, apparently permanent and growing "underclass," uneducated and unskilled, mostly black and Hispanic, and outside the economic mainstream. The gap between their skills and available jobs will grow as work becomes more dependent on high technology.

Individuals will continue to acquire the skills necessary to escape the underclass, but a growing percentage will be left behind. Nor will those left find much help from the society at large: government is being curtailed, and the consensus is that enough has been done already for minorities. The resulting joblessness and hopelessness are hard enough to take when the economy is struggling. They are likely to become intolerable during a recovery. Thus BERI's forecast:

"Economic recovery begins in early 1983, and serious urban rioting occurs when poor and unemployed in the center-cities realize that they are once again being excluded from the new and growing wealth. These demonstrations occur in cities experiencing renewal or rapid growth, such as Houston or Los Angeles, as well as in the old industrial areas of the North. Government reaction and public consensus favor a strong response, with police and national guard intervention causing widespread bloodshed.

"Unlike the urban riots of the 1960s, which called attention to a group about which most Americans had been unaware . . . these uprisings of 1983 are forcibly put down. Attention is directed toward protecting property rather than toward seeking the causes and their remedies. Social programs are considered to be costly and ineffective."

It isn't a pretty picture. But it will take more than crossed fingers to keep it from proving an accurate one..