WHEN Jane Collins suggested six months ago that her son get tested for the AIDS virus, the 18-year-old would have nothing to do with it.Last week, in the wake of Earvin "Magic" Johnson's announcement that he had contracted the HIV, the youth led his mother to a testing clinic here barely a jump shot away from the Forum, where the basketball star became a legend. "Now my boy is signing up his friends and telling them they can't keep their heads in the sand any longer," says Mrs. Collins (not her real name). More than any celebrity, statistic, or "consciousness-raising" event in a decade, "Magic" Johnson has changed the way Americans think about AIDS. In six short days he has punctured old myths, raised new concerns, and revivified the debate over how best to control the spread of a disease that has claimed 125,000 lives since 1981. Because his athletic achievement and prominence touch corners of society accessible in few other ways, activists are calling the event a watershed in national awareness. From inner-city playgrounds to classrooms to the halls of Congress, people are talking more openly about curbing sexual promiscuity, distributing condoms, and whether the federal government is doing enough to stop one of the nation's premier health problems. Yet those who have been on the front lines in the AIDS battle for years caution against excessive fear - or short-lived concern. "We have to quiet hysteria with education that is ongoing and consistent," says Bishop Carl Bean, founder of the Minority AIDS Project here. "We can't go back to business as usual after the headlines die down." Activists say Mr. Johnson's announcement is driving home the message that the AIDS virus isn't limited to homosexuals and drug users, but also poses a growing risk to heterosexuals. Statistics show the disease is taking a particular toll on inner-city blacks and Hispanics, a group Johnson promises to reach out to. "The epidemic is more and more one of the urban poor," says Scott Burris, a professor of law at Temple University and author of a book on AIDS. As many as a million Americans and another 10 million people worldwide are estimated to be infected with HIV (human immunodeficiency virus). The Centers for Disease Control in Atlanta report 195,700 AIDS cases in the US. Exposure in 59 percent of those cases resulted from homosexual contact, the agency says, and 22 percent were the result of intravenous drug use. While only 6 percent resulted from heterosexual contact, those numbers are rising rapidly: Between 1989 and 1990, the incidence of AIDS cases among heterosexuals increased 40 percent. Magic Johnson began his new ambassadorial role by appearing on the Arsenio Hall show, preaching "safe sex" and admonishing that "we don't have to run from [the disease]." His message is expected to resonate with the legions of teenagers for whom he is a story-book hero and role model. School yards and classrooms crackle with concern about the beloved athlete with the jack-o'-lantern grin. "Magic Johnson pushes us to another threshold" of awareness, says James Slack, a public administration specialist at Cleveland State University who has written a book on AIDS. Activists also hope Johnson's involvement in the crusade will free up more money from Uncle Sam. Some $3.7 billion in federal funding was spent on AIDS prevention, research, and treatment last year. Yet, of $880 million Congress authorized for cities and states to fight the disease under the Ryan White Care Act, less than half has been appropriated. "This presents an opportunity for everyone from parents to the president to start talking about AIDS and act on it," says Carisa Cunningham of the AIDS Action Council in Washington, D.C. Differences exist over the disbursement of dollars that are available. Bishop Bean, for instance, complains that his project, which caters mainly to inner-city blacks and Hispanics, receives 1/10th the public money of the crosstown AIDS Project of Los Angeles. "This ... shows the disease does not discriminate between black, white, gay, and Hispanics," he says. "Why should the funding?" Other areas likely to receive fresh scrutiny as a result of the Johnson announcement: Education. At least 31 states now mandate that schools provide some form of AIDS education, though there are widely differing views on how it should be presented. Some religious groups, for example, want heavier stress on abstinence, while AIDS activists and others think that is unrealistic when children as young as 12 are becoming sexually active. They urge more stress on "safe sex," including the distribution of condoms in schools, both of which are currently being debated in San Francisco and Los Angeles. Testing. Clinics across the country continue to be flooded with inquiries from heterosexuals and others who have not until now considered themselves "high risk." Officials welcome the concern but caution against panic. The new awareness may also spur a debate over the idea of mandatory testing in contact sports. Civil libertarians have resolutely opposed such testing among health care workers.