THE FIRST decade of the AIDS epidemic is drawing to a close, with no clear understanding of the full scope of the disease’s impact. The present situation--95,000 AIDS cases reported in the United States in mid-1989--is bad enough, but not nearly so troubling as what inevitably lies ahead in the next five years. The Centers for Disease Control (CDC) estimate that AIDS has already infected between 945,000 and 1.4 million Americans; by 1993, say the CDC, there will be 450,000 fullblown AIDS cases in the U.S. Even as the rate of infection among homosexual men declines, increased rates of viral transmission through intravenous drug use and heterosexual sex, disproportionately among blacks and Hispanics, will push these figures higher.