BOSTON, NOV. 28 -- About one in 500 U.S. college students is infected with the AIDS virus, and further spread of the disease is likely on campuses unless students change their sexual habits, according to the federal Centers for Disease Control.

"Risky behaviors are occurring, and now we know we have the infection," said Dr. Helene D. Gayle, who directed the study. "It is cause for concern and appropriate attention."

The CDC study is the first nationwide attempt to judge the presence of HIV on college campuses, said coauthor Dr. Richard P. Keeling of the American College Health Association. It shows that the virus probably is about as common there as in the public at large.

However, the researchers cautioned that AIDS still could spread dramatically among college students, just as some other sexually transmitted diseases have done.

"I think probably the most important thing from this study is that it shows us the potential," said Keeling, who also runs the student health service at the University of Virginia. "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. The study found that 30 students, or two-tenths of 1 percent of the students, were infected with the virus. At 10 of the 19 campuses, the survey found no AIDS infections.

The survey, published in Thursday's New England Journal of Medicine, also found that students over age 24 were seven times more likely than younger students to be infected.