JOHN Sperling, a man who has been called the Howard Hughes of biotechnology, has $3 billion and a dream: to retard aging and extend human longevity. According to a recent article in Wired magazine, he intends to found an endowment generating at least $150 million a year for biotech research. “I am 100 percent for human enhancement!” he told the magazine. “The more you can get, the better! What do we want? To improve the quality of human life to maximize happiness, right?” His dream is the worry of President Bush’s Council on Bioethics, which is headed by Leon R. Kass.