BLACK America, despite serious problems, has made dramatic strides during the past few decades in education, income, health, and politics.These are some of the major conclusions from an extensive study, "African Americans in the 1990s," released Thursday by the Population Reference Bureau Inc. A few quick facts: * The black middle class is booming. The number of affluent African-American families with incomes over $50,000 rose from 266,000 in 1967 to over 1 million in 1989. * College-educated blacks have enjoyed rapidly rising incomes, with young, college-educated black families now earning, on average, 93 percent of the incomes of comparable whites. * The number of blacks holding elected office climbed 47 percent during the 1980s, from 4,900 to 7,200. * Infant mortality rates for black children have fallen to only one-fourth the level they were in 1940, though there is still substantial room for improvement. William O'Hare, head of Population and Policy Research at the Urban Research Institute, University of Louisville, was one of the report's authors. He observes: "It's a different ballgame than it was a generation ago. For example, in 1940, 95 percent of all blacks were below the poverty level. Even in 1950 or 1960, if blacks were not poor, they had been raised in a poor family." Today, there is still a large population of blacks in poverty, but there is also "a large segment of blacks who are in the middle class or who are wealthy," Dr. O'Hare says. "From the beginning, these [middle class] people had good schools and other opportunities that were not available to their ancestors." However, the rise of the black middle class has created an economic fault line, which separates the newly affluent from millions of their black brethren who are still living in poverty. This economic separation "could lead to fragmentation and divisiveness" among blacks, O'Hare says. The professor says this already seems apparent in black attitudes toward Clarence Thomas, the black nominee to the United States Supreme Court. Younger, affluent blacks widely support the nomination, while older African Americans who grew up poor are suspicious of Judge Thomas's conservative views. Meanwhile, other changes taking place seem less sanguine for blacks, according to this report, which was also written by Taynia Mann and Kelvin Pollard, research demographers at the Population Reference Bureau, and Mary Kent, editor of the bureau's quarterly journal, "Population Bulletin." The PRB is a nonprofit educational organization based in Washington, D.C. Blacks, for example, had always been the nation's largest minority - the focal point of political reform and economic assistance. All that may be changing. By early in the 21st century, Hispanics will be America's largest minority. Hispanics are currently growing at a rate four times as fast as the black population, while another booming minority, Asian-Americans, is growing at a rate eight times as fast as blacks. O'Hare says the rise of other minorities could dampen enthusiasm among majority whites to support programs like affirmative action. It could also create tensions, like those already apparent, between blacks, Hispanics, and Asians in cities like Miami, New York, and Washington. Even middle-class blacks may be less interested in coming years in helping the poor. Today, the number of black suburbanites has risen to 8.2 million, up 50 percent since 1980. Like other suburbanites, they have left many urban problems behind, and are focused on family, schools, and jobs in their new environment. Meanwhile, African-Americans left in the urban core of large cities such as Detroit (where they comprise 76 percent of the population), Baltimore (59 percent), and Chicago (39 percent) are often overwhelmed by crime, disease, and teen births which make the situation even more difficult. "The disproportionately high rate of teen childbearing in the African-American community exacerbates many social problems," the report notes. "Health problems, high infant mortality, educational deficiencies, long-term welfare dependency, and poverty are among the consequences risked by teens who have babies." The urban cores' problems with crime, illegal drugs, and AIDS are well documented. These problems help to explain why black men are 7.6 times more likely to be murdered than white men, and why black women are nearly nine times more likely to contract AIDS than white women. O'Hare says AIDS and homicide are the reasons that life expectancies actually declined for blacks overall in the late 1980s. Two other factors also make it harder for blacks to realize the American dream. One is housing segregation. Blacks are twice as likely to live in segregated housing as Hispanics or Asians. The other is intermarriage. Very few blacks marry whites (3 percent), but Hispanics and Asians marry whites in growing numbers (currently 17 percent for each group). Intermarriage, together with housing integration, is smoothing the transition of these minorities into the American mainstream, while millions of blacks are left behind.