The first nationwide survey of AIDS at colleges shows that the virus has gained a small but worrisome foothold on America's campuses, infecting about one in every 500 students.

Based on this and other data, the federal Centers for Disease Control estimates that between 25,000 and 35,000 of the nation's 13 million college students are infected with the AIDS virus. That makes AIDS about as common on university campuses as it is elsewhere in American life, the study shows."This is both good news and bad news," said Leighton Ku, a public health specialist at the Urban Institute in Washington. "It's good that it's not sky-high, as some had feared. But it's bad that it's there at all." While its presence among college students is still small, experts fear AIDS could spread substantially.

"I think probably the most important thing from this study is that it shows us the potential," said Dr. Richard P. Keeling of the American College Health Association. "The combination of a sexually transmitted disease tossed into campus behavior has the potential for very serious consequences in the future. It also shows us we have an opportunity to prevent that."

The study was based on random testing of blood samples drawn from 16,863 students at 19 schools, most of them large state universities. Thirty students - or two-tenths of 1 percent - were found to be infected. All but two were men.

Among other results of the study, published in Thursday's New England Journal of Medicine: Those over age 24 were seven times more likely than younger students to be infected; and at 10 of the 19 campuses, the survey turned up no AIDS infections.